/* ============================================
   [11] CSS CUSTOM PROPERTIES — BatchCalc theme.
   Dark navy with blue-to-orange gradient accents.
   One :root, easy to retheme later.
   ============================================ */
:root {
    --bg: #0a1020;
    --bg-surface: #111a30;
    --bg-elevated: #18233e;
    --bg-input: #0d1426;
    --text: #e8ecf5;
    --text-muted: #8a96b3;
    --text-dim: #5a6685;
    --accent-blue: #6f9bff;
    --accent-orange: #f5a572;
    --accent-blue-soft: rgba(111, 155, 255, 0.15);
    --accent-orange-soft: rgba(245, 165, 114, 0.15);
    --border: #1f2c4a;
    --border-strong: #2a3a5e;
    --danger: #ff7a85;
    --success: #6fd9a8;
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
    --radius: 0.6rem;
    --radius-lg: 0.85rem;
    --transition: 180ms ease;
    --gradient-text: linear-gradient(90deg, #6f9bff 0%, #f5a572 100%);
    --gradient-bg: radial-gradient(ellipse at top right, rgba(111, 155, 255, 0.12) 0%, transparent 60%);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

/* Light theme override */
:root[data-theme="light"] {
    --bg: #f5f6fa;
    --bg-surface: #ffffff;
    --bg-elevated: #edf0f7;
    --bg-input: #f0f2f8;
    --text: #1a1d2e;
    --text-muted: #5a6078;
    --text-dim: #8a8fa8;
    --accent-blue: #3b6de0;
    --accent-orange: #d07830;
    --accent-blue-soft: rgba(59, 109, 224, 0.1);
    --accent-orange-soft: rgba(208, 120, 48, 0.1);
    --border: #d8dce8;
    --border-strong: #c0c6d8;
    --danger: #d43b48;
    --success: #2e9968;
    --shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
    --gradient-text: linear-gradient(90deg, #3b6de0 0%, #d07830 100%);
    --gradient-bg: radial-gradient(ellipse at top right, rgba(59, 109, 224, 0.06) 0%, transparent 60%);
    color-scheme: light;
}

html { color-scheme: dark; }
:root[data-theme="light"] { color-scheme: light; }
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
    background: var(--bg);
    background-image: var(--gradient-bg);
    background-attachment: fixed;
    color: var(--text);
    line-height: 1.5;
    min-height: 100vh;
    overflow: hidden;
}

/* Themed scrollbars — no default browser bars */
*::-webkit-scrollbar { width: 10px; height: 10px; }
*::-webkit-scrollbar-track { background: transparent; }
*::-webkit-scrollbar-thumb {
    background: var(--border-strong);
    border-radius: 10px;
    border: 2px solid transparent;
    background-clip: padding-box;
}
*::-webkit-scrollbar-thumb:hover { background-color: var(--accent-blue); background-clip: padding-box; }
* { scrollbar-width: thin; scrollbar-color: var(--border-strong) transparent; }

/* Accessibility — visible focus only for keyboard */
:focus-visible { outline: 2px solid var(--accent-blue); outline-offset: 2px; }
:focus:not(:focus-visible) { outline: none; }

/* Skip link */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0.5rem;
    background: var(--accent-blue);
    color: var(--bg);
    padding: 0.5rem 1rem;
    border-radius: 0 0 var(--radius) var(--radius);
    z-index: 100;
    text-decoration: none;
    font-weight: 600;
}
.skip-link:focus { top: 0; }

/* Screen-reader only */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* ============================================
   LAYOUT — sidebar + main
   ============================================ */
#app {
    display: grid;
    grid-template-columns: 240px 1fr;
    height: 100vh;
    width: 100vw;
}

/* SIDEBAR */
#sidebar {
    background: var(--bg-surface);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}
.brand {
    padding: 1.1rem 1.1rem 0.9rem;
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 0.65rem;
}
.brand-logo {
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}
.brand-logo svg { width: 100%; height: 100%; display: block; }
.brand-name {
    font-weight: 800;
    font-size: 0.95rem;
    letter-spacing: 0.08em;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
    line-height: 1.15;
}
.brand-sub {
    display: block;
    font-size: 0.68rem;
    color: var(--text-muted);
    font-weight: 500;
    margin-top: 0.05rem;
}
#sidebar nav {
    flex: 1;
    overflow-y: auto;
    padding: 0.75rem 0.5rem;
}
.nav-group-label {
    font-size: 0.68rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-dim);
    padding: 0.75rem 0.75rem 0.4rem;
    font-weight: 600;
}
.nav-item {
    display: flex;
    align-items: center;
    gap: 0.7rem;
    padding: 0.55rem 0.75rem;
    border-radius: var(--radius);
    color: var(--text-muted);
    font-size: 0.88rem;
    cursor: pointer;
    background: none;
    border: none;
    width: 100%;
    text-align: left;
    transition: background var(--transition), color var(--transition);
    font-family: inherit;
    margin-bottom: 0.15rem;
}
.nav-item:hover { background: var(--accent-blue-soft); color: var(--text); }
.nav-item.active {
    background: var(--accent-blue-soft);
    color: var(--accent-blue);
    font-weight: 600;
}
.nav-icon { width: 18px; height: 18px; flex-shrink: 0; opacity: 0.85; }
.nav-item.coming-soon { opacity: 0.55; }
.nav-item .badge {
    margin-left: auto;
    font-size: 0.62rem;
    padding: 0.1rem 0.45rem;
    background: var(--accent-orange-soft);
    color: var(--accent-orange);
    border-radius: 999px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}
.sidebar-footer {
    padding: 0.75rem;
    border-top: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}
.lang-select {
    width: 100%;
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text);
    padding: 0.5rem 0.6rem;
    border-radius: var(--radius);
    font-size: 0.85rem;
    font-family: inherit;
    cursor: pointer;
}
.lang-select:focus-visible { border-color: var(--accent-blue); }

/* MAIN */
#main {
    overflow-y: auto;
    padding: 1.5rem 2rem 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}
#main-content {
    flex: 1;
    padding-bottom: 2rem;
}
.app-tagline {
    font-size: 0.85rem;
    color: var(--text-muted);
    font-style: italic;
    margin: 0 0 1.25rem 0;
    padding: 0.65rem 1rem;
    border-left: 2px solid;
    border-image: linear-gradient(180deg, var(--accent-blue), var(--accent-orange)) 1;
    background: linear-gradient(90deg, var(--accent-blue-soft), transparent 60%);
    border-radius: 0 var(--radius) var(--radius) 0;
}
.app-footer {
    margin-top: auto;
    padding: 1.25rem 0 1.5rem;
    border-top: 1px solid var(--border);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    font-size: 0.82rem;
    color: var(--text-muted);
}
.app-footer a {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    color: var(--text);
    text-decoration: none;
    font-weight: 600;
    padding: 0.3rem 0.65rem;
    border-radius: var(--radius);
    transition: all var(--transition);
    border: 1px solid transparent;
}
.app-footer a:hover {
    color: var(--accent-blue);
    background: var(--accent-blue-soft);
    border-color: var(--accent-blue);
}
.app-footer a:focus-visible {
    outline: 2px solid var(--accent-blue);
    outline-offset: 2px;
}
.footer-logo { line-height: 0; flex-shrink: 0; }
.footer-sep { color: var(--text-dim); }
.footer-license {
    color: var(--text-muted);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.78rem;
    padding: 0.25rem 0.5rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    transition: all var(--transition);
}
.footer-license:hover {
    color: var(--accent-orange);
    border-color: var(--accent-orange);
    background: var(--accent-orange-soft);
}
.footer-license:focus-visible {
    outline: 2px solid var(--accent-blue);
    outline-offset: 2px;
}

/* Mobile: footer wraps cleanly */
@media (max-width: 480px) {
    .app-footer {
        flex-wrap: wrap;
        font-size: 0.75rem;
        gap: 0.4rem;
    }
}
.page-header {
    margin-bottom: 1.25rem;
}
.page-title {
    font-size: 1.7rem;
    font-weight: 700;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
    margin-bottom: 0.2rem;
    line-height: 1.2;
}
.page-subtitle { color: var(--text-muted); font-size: 0.95rem; }

/* ============================================
   CALCULATOR
   ============================================ */
.calc-layout {
    display: grid;
    grid-template-columns: minmax(0, 520px) minmax(280px, 1fr);
    gap: 1.25rem;
    align-items: start;
    max-width: 1200px;
}
/* Standard mode: narrower calculator since no function block */
.calc-layout.standard {
    grid-template-columns: minmax(0, 380px) minmax(280px, 1fr);
}
/* The STD/SCI toggle pills sit together with no gap, like a segmented control */
.mode-toggle {
    display: inline-flex;
    gap: 0;
    border-radius: 999px;
    background: var(--bg-elevated);
    padding: 2px;
    border: 1px solid var(--border);
}
.mode-toggle .pill {
    border: none;
    background: transparent;
    border-radius: 999px;
    padding: 0.18rem 0.7rem;
}
.mode-toggle .pill.active {
    background: var(--accent-blue-soft);
    border-color: transparent;
}
.calculator {
    background: var(--bg-surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 1.1rem;
    box-shadow: var(--shadow);
}

/* Display */
.display {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.85rem 1rem;
    margin-bottom: 0.9rem;
    min-height: 110px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    overflow: hidden;
}
.display-meta {
    display: flex;
    gap: 0.4rem;
    align-items: center;
    font-size: 0.7rem;
    flex-wrap: wrap;
    margin-bottom: 0.4rem;
}
.pill {
    background: var(--bg-elevated);
    color: var(--text-dim);
    padding: 0.18rem 0.55rem;
    border-radius: 999px;
    font-weight: 600;
    border: 1px solid var(--border);
    cursor: pointer;
    font-family: inherit;
    font-size: 0.7rem;
    transition: all var(--transition);
}
.pill:hover { color: var(--text); }
.pill.active {
    color: var(--accent-blue);
    background: var(--accent-blue-soft);
    border-color: var(--accent-blue);
}
.pill.mem-active {
    color: var(--accent-orange);
    background: var(--accent-orange-soft);
    border-color: var(--accent-orange);
}
.display-expression {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.95rem;
    color: var(--text-muted);
    text-align: right;
    overflow-x: auto;
    white-space: nowrap;
    min-height: 1.4em;
    direction: rtl;
}
.display-result {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 2rem;
    font-weight: 600;
    color: var(--text);
    text-align: right;
    overflow-x: auto;
    white-space: nowrap;
    line-height: 1.2;
    direction: rtl;
}
.display-result.error { color: var(--danger); font-size: 1.3rem; }

/* Keypad — split into a function block (top) and a number+ops block (bottom)
   to mimic a real scientific calculator like a Casio fx-991. */
.keypad {
    display: flex;
    flex-direction: column;
    gap: 0.55rem;
}
.keypad-fn {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 0.4rem;
}
.keypad-bottom {
    display: grid;
    grid-template-columns: 4fr 1fr;
    gap: 0.4rem;
    padding-top: 0.55rem;
    border-top: 1px solid var(--border);
}
.keypad-nums {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(5, 1fr);
    gap: 0.4rem;
}
.keypad-ops {
    display: grid;
    grid-template-columns: 1fr;
    grid-template-rows: repeat(5, 1fr);
    gap: 0.4rem;
}
.key.zero-wide { grid-column: span 2; }
.key {
    padding: 0.78rem 0.3rem;
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    color: var(--text);
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    font-family: inherit;
    transition: background var(--transition), border-color var(--transition), transform 80ms ease;
    user-select: none;
    min-height: 46px;
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
}
.key:hover { background: var(--bg-input); border-color: var(--border-strong); }
.key:active { transform: scale(0.96); }
.key.fn { color: var(--accent-blue); font-weight: 600; font-size: 0.82rem; }
.key.op {
    color: var(--accent-orange);
    font-weight: 700;
    font-size: 1.15rem;
    background: var(--bg-input);
    border-color: var(--border-strong);
}
.key.op:hover { background: var(--accent-orange-soft); border-color: var(--accent-orange); }
.key.num {
    font-size: 1.15rem;
    font-weight: 600;
    background: var(--bg-input);
    border-color: var(--border-strong);
}
.key.num:hover { background: var(--bg-elevated); border-color: var(--accent-blue); }
.key.equals {
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-orange));
    color: var(--bg);
    border-color: transparent;
    font-weight: 800;
    font-size: 1.15rem;
}
.key.equals:hover { filter: brightness(1.1); }
.key.danger { color: var(--danger); font-weight: 600; }
.key.mem { color: var(--accent-orange); font-size: 0.8rem; font-weight: 600; }
.key.wide-2 { grid-column: span 2; }
.key sup { font-size: 0.65em; }
.key sub { font-size: 0.65em; }

/* Side panels */
.side-panel {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}
.panel {
    background: var(--bg-surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    overflow: hidden;
    display: flex;
    flex-direction: column;
}
.panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.7rem 0.9rem;
    border-bottom: 1px solid var(--border);
    background: var(--bg-elevated);
}
.panel-header h2 {
    font-size: 0.78rem;
    font-weight: 700;
    color: var(--text);
    text-transform: uppercase;
    letter-spacing: 0.06em;
}
.panel-header button {
    background: none;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    font-size: 0.72rem;
    padding: 0.25rem 0.55rem;
    border-radius: var(--radius);
    transition: color var(--transition), background var(--transition);
    font-family: inherit;
    font-weight: 600;
}
.panel-header button:hover { color: var(--danger); background: var(--bg-input); }
.panel-body {
    overflow-y: auto;
    flex: 1;
    padding: 0.5rem;
    max-height: 360px;
}
.history-empty, .memory-empty {
    text-align: center;
    color: var(--text-dim);
    font-size: 0.85rem;
    padding: 1.5rem 1rem;
}
.history-item {
    padding: 0.55rem 0.7rem;
    border-radius: var(--radius);
    cursor: pointer;
    transition: background var(--transition), border-color var(--transition);
    border: 1px solid transparent;
    margin-bottom: 0.25rem;
    background: none;
    width: 100%;
    text-align: right;
    font-family: inherit;
    color: inherit;
}
.history-item:hover { background: var(--bg-elevated); border-color: var(--border); }
.history-expr {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.78rem;
    color: var(--text-muted);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    text-align: right;
}
.history-result {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.95rem;
    color: var(--accent-blue);
    font-weight: 600;
    margin-top: 0.15rem;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    text-align: right;
}
.history-row {
    position: relative;
    margin-bottom: 0.25rem;
}
.history-row .history-item { padding-right: 2rem; }
.history-note {
    font-size: 0.72rem;
    color: var(--accent-orange);
    font-weight: 600;
    margin-bottom: 0.15rem;
    text-align: left;
    direction: ltr;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}
.history-note-btn {
    position: absolute;
    top: 50%;
    right: 0.4rem;
    transform: translateY(-50%);
    width: 26px;
    height: 26px;
    background: transparent;
    border: 1px solid transparent;
    color: var(--text-dim);
    border-radius: var(--radius);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
}
.history-row:hover .history-note-btn,
.history-note-btn:focus-visible { color: var(--accent-orange); border-color: var(--border); }
.history-note-btn:hover { background: var(--accent-orange-soft); }
/* Touch devices: pencil always visible since :hover doesn't fire reliably */
@media (hover: none) {
    .history-note-btn { color: var(--text-muted); }
}
.history-note-editor {
    display: flex;
    gap: 0.35rem;
    margin-top: 0.35rem;
    align-items: stretch;
}
.history-note-editor .tool-input {
    flex: 1;
    min-width: 0;
    font-size: 0.85rem;
    padding: 0.4rem 0.6rem;
    font-family: inherit;
}
.history-note-editor .tool-btn {
    font-size: 0.78rem;
    padding: 0.35rem 0.65rem;
    flex-shrink: 0;
}
.memory-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.5rem 0.7rem;
    border-radius: var(--radius);
    background: var(--bg-elevated);
    margin-bottom: 0.3rem;
}
.memory-label {
    font-size: 0.72rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-weight: 600;
}
.memory-value {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.9rem;
    color: var(--text);
    font-weight: 600;
}

/* Coming-soon stub page */
.stub {
    background: var(--bg-surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 3rem 2rem;
    text-align: center;
    box-shadow: var(--shadow);
}
.stub-icon { font-size: 2.5rem; margin-bottom: 0.75rem; }
.stub h2 {
    font-size: 1.3rem;
    margin-bottom: 0.5rem;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}
.stub p { color: var(--text-muted); max-width: 32rem; margin: 0 auto; }

/* Settings page */
.settings-card {
    background: var(--bg-surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 1.25rem;
    margin-bottom: 1rem;
}
.settings-card h3 {
    font-size: 0.78rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-muted);
    margin-bottom: 0.85rem;
    font-weight: 700;
}
.setting-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.6rem 0;
    border-bottom: 1px solid var(--border);
}
.setting-row:last-child { border-bottom: none; }
.setting-label { color: var(--text); font-size: 0.92rem; }
.setting-desc { color: var(--text-muted); font-size: 0.8rem; margin-top: 0.2rem; }

/* ============================================
   SHARED PAGE COMPONENTS — used by every new tab
   ============================================ */
.tool-card {
    background: var(--bg-surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 1.25rem;
    margin-bottom: 1rem;
    box-shadow: var(--shadow);
}
.tool-card h3 {
    font-size: 0.78rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-muted);
    margin-bottom: 0.85rem;
    font-weight: 700;
}
.tool-row {
    display: flex;
    gap: 0.75rem;
    align-items: center;
    margin-bottom: 0.75rem;
    flex-wrap: wrap;
}
.tool-row:last-child { margin-bottom: 0; }
.tool-input, .tool-select, .tool-textarea {
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text);
    padding: 0.55rem 0.75rem;
    border-radius: var(--radius);
    font-size: 0.95rem;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    transition: border-color var(--transition);
    outline: none;
}
.tool-input:focus, .tool-select:focus, .tool-textarea:focus { border-color: var(--accent-blue); }
.tool-input { flex: 1; min-width: 0; }
.tool-select {
    font-family: inherit;
    cursor: pointer;
    min-width: 140px;
}
.tool-textarea {
    width: 100%;
    min-height: 80px;
    resize: vertical;
    line-height: 1.5;
}
.tool-label {
    color: var(--text-muted);
    font-size: 0.85rem;
    font-weight: 600;
    min-width: 90px;
}
.tool-btn {
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text);
    padding: 0.55rem 1rem;
    border-radius: var(--radius);
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
}
.tool-btn:hover { border-color: var(--accent-blue); color: var(--accent-blue); }
.tool-btn.primary {
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-orange));
    color: var(--bg);
    border-color: transparent;
}
.tool-btn.primary:hover { filter: brightness(1.1); color: var(--bg); }
.tool-btn.danger { color: var(--danger); }
.tool-btn.danger:hover { border-color: var(--danger); color: var(--danger); }

.result-box {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.75rem 1rem;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 1.1rem;
    color: var(--accent-blue);
    word-break: break-all;
    min-height: 2.5rem;
}
.result-box.large {
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
    padding: 1.25rem;
}
.result-box.error { color: var(--danger); }
.result-box.muted { color: var(--text-dim); font-size: 0.95rem; }

.stat-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 0.5rem;
}
.stat-tile {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.75rem 1rem;
}
.stat-tile-label {
    font-size: 0.7rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    font-weight: 600;
    margin-bottom: 0.25rem;
}
.stat-tile-value {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 1.05rem;
    color: var(--text);
    font-weight: 600;
}

/* Tab strip — used inside pages that need sub-modes */
.tab-strip {
    display: flex;
    gap: 0.4rem;
    margin-bottom: 1rem;
    border-bottom: 1px solid var(--border);
    padding-bottom: 0.4rem;
    flex-wrap: wrap;
}
.tab-strip button {
    background: none;
    border: 1px solid transparent;
    color: var(--text-muted);
    padding: 0.45rem 0.9rem;
    border-radius: var(--radius);
    font-family: inherit;
    font-size: 0.88rem;
    cursor: pointer;
    transition: all var(--transition);
}
.tab-strip button:hover { color: var(--text); }
.tab-strip button.active {
    color: var(--accent-blue);
    background: var(--accent-blue-soft);
    border-color: var(--accent-blue);
}

/* ============================================
   UNIT CONVERTER
   ============================================ */
.unit-layout {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 0.75rem;
    align-items: end;
}
.unit-side label {
    display: block;
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-bottom: 0.3rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}
.unit-side .tool-input { width: 100%; margin-bottom: 0.4rem; font-size: 1.2rem; padding: 0.65rem 0.85rem; }
.unit-side .tool-select { width: 100%; }
.unit-swap {
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--accent-blue);
    width: 40px;
    height: 40px;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 1.2rem;
    margin-bottom: 0.4rem;
    transition: all var(--transition);
}
.unit-swap:hover { background: var(--accent-blue-soft); transform: rotate(180deg); }

/* ============================================
   PROGRAMMER MODE
   ============================================ */
.prog-display {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1rem;
    margin-bottom: 1rem;
}
.prog-row {
    display: grid;
    grid-template-columns: 60px 1fr;
    gap: 0.75rem;
    align-items: center;
    padding: 0.5rem 0;
    border-bottom: 1px dashed var(--border);
}
.prog-row:last-child { border-bottom: none; }
.prog-base {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.75rem;
    color: var(--accent-orange);
    font-weight: 700;
    letter-spacing: 0.05em;
}
.prog-value {
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 1.05rem;
    color: var(--text);
    word-break: break-all;
}
.prog-bits {
    display: grid;
    grid-template-columns: repeat(8, 1fr);
    gap: 0.25rem;
    margin-top: 0.5rem;
}
.prog-bit {
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text-dim);
    text-align: center;
    padding: 0.4rem 0;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    border-radius: 4px;
    transition: all var(--transition);
}
.prog-bit.on { background: var(--accent-blue-soft); color: var(--accent-blue); border-color: var(--accent-blue); }
.prog-bit:hover { border-color: var(--accent-blue); }
.prog-bit-index {
    font-size: 0.6rem;
    color: var(--text-dim);
    text-align: center;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    margin-top: 0.15rem;
}

/* ============================================
   EQUATION SOLVER
   ============================================ */
.eq-form {
    display: flex;
    gap: 0.5rem;
    align-items: center;
    flex-wrap: wrap;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 1.1rem;
}
.eq-form .tool-input {
    width: 70px;
    text-align: center;
    font-size: 1.05rem;
    flex: 0 0 auto;
}
.eq-form .eq-token { color: var(--text-muted); }

.solutions {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}
.solution {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.75rem 1rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
}
.solution-label { color: var(--accent-orange); font-weight: 700; }
.solution-value { color: var(--accent-blue); font-size: 1.1rem; font-weight: 600; }

/* ============================================
   MATRIX
   ============================================ */
.matrix-grid {
    display: inline-grid;
    gap: 0.35rem;
    background: var(--bg-input);
    padding: 0.6rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    margin: 0.5rem 0;
}
.matrix-cell {
    width: 60px;
    height: 38px;
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text);
    border-radius: 4px;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.9rem;
    text-align: center;
    outline: none;
    transition: border-color var(--transition);
}
.matrix-cell:focus { border-color: var(--accent-blue); }
.matrix-cell.readonly { background: var(--bg-input); color: var(--accent-blue); }
.matrix-size {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-muted);
    font-size: 0.85rem;
}
.matrix-size input {
    width: 60px;
    text-align: center;
}

/* ============================================
   STATISTICS
   ============================================ */
.stats-input { font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace; font-size: 0.9rem; }
.regression-table {
    background: var(--bg-input);
    border-radius: var(--radius);
    border: 1px solid var(--border);
    padding: 0.75rem 1rem;
    margin-top: 0.5rem;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
    font-size: 0.95rem;
}

/* ============================================
   GRAPHING
   ============================================ */
.graph-canvas-wrap {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.5rem;
    margin-bottom: 1rem;
    cursor: grab;
    user-select: none;
    overflow: hidden;
    position: relative;
}
.graph-canvas-wrap.panning { cursor: grabbing; }
.graph-canvas-wrap svg {
    width: 100%;
    height: auto;
    display: block;
    touch-action: none;
}
.graph-overlay {
    position: absolute;
    bottom: 0.75rem;
    right: 0.75rem;
    display: flex;
    gap: 0.3rem;
    background: var(--bg-surface);
    opacity: 0.92;
    backdrop-filter: blur(4px);
    padding: 0.35rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
}
.graph-overlay button {
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text);
    width: 32px;
    height: 32px;
    border-radius: 4px;
    cursor: pointer;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 700;
    transition: all var(--transition);
}
.graph-overlay button:hover { border-color: var(--accent-blue); color: var(--accent-blue); }
.graph-info {
    display: flex;
    gap: 1.25rem;
    flex-wrap: wrap;
    font-size: 0.78rem;
    color: var(--text-muted);
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
}

/* ============================================
   CURRENCY
   ============================================ */
.rate-banner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.75rem;
    padding: 0.75rem 1rem;
    border-radius: var(--radius);
    margin-bottom: 1rem;
    font-size: 0.88rem;
    font-weight: 500;
    flex-wrap: wrap;
}
.rate-banner.warning {
    background: rgba(245, 165, 114, 0.1);
    border: 1px solid var(--accent-orange);
    color: var(--accent-orange);
}
.rate-banner.danger {
    background: rgba(255, 122, 133, 0.1);
    border: 1px solid var(--danger);
    color: var(--danger);
}
.rate-info {
    margin-top: 0.85rem;
    padding-top: 0.75rem;
    border-top: 1px solid var(--border);
}
.rate-line {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
    font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace;
}
.rate-meta {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    font-size: 0.78rem;
    color: var(--text-dim);
    flex-wrap: wrap;
}
.rate-source {
    padding: 0.18rem 0.6rem;
    border-radius: 999px;
    font-weight: 700;
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    border: 1px solid var(--border);
}
.rate-source.live {
    background: rgba(111, 217, 168, 0.12);
    color: var(--success);
    border-color: var(--success);
}
.rate-source.cache {
    background: var(--accent-blue-soft);
    color: var(--accent-blue);
    border-color: var(--accent-blue);
}
.rate-source.static {
    background: var(--accent-orange-soft);
    color: var(--accent-orange);
    border-color: var(--accent-orange);
}
.rate-date { font-family: 'SF Mono', Menlo, Monaco, 'Courier New', monospace; }
.tool-btn.small {
    padding: 0.35rem 0.7rem;
    font-size: 0.78rem;
    margin-left: auto;
}

/* Toast */
#toast-container {
    position: fixed;
    bottom: 1.5rem;
    right: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    z-index: 50;
    pointer-events: none;
}
.toast {
    background: var(--bg-elevated);
    border: 1px solid var(--border-strong);
    color: var(--text);
    padding: 0.7rem 1rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    font-size: 0.88rem;
    pointer-events: auto;
    opacity: 0;
    transform: translateY(0.5rem);
    transition: opacity var(--transition), transform var(--transition);
    max-width: 320px;
}
.toast.show { opacity: 1; transform: translateY(0); }

/* ============================================
   TOP BAR (mobile only) — hamburger + brand + page title
   ============================================ */
#topbar {
    display: none;
    position: sticky;
    top: 0;
    z-index: 30;
    background: var(--bg-surface);
    border-bottom: 1px solid var(--border);
    padding: 0.55rem 0.75rem;
    align-items: center;
    gap: 0.6rem;
}
.topbar-btn {
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text);
    width: 40px;
    height: 40px;
    border-radius: var(--radius);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all var(--transition);
}
.topbar-btn:hover { border-color: var(--accent-blue); color: var(--accent-blue); }
.topbar-brand {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    flex: 1;
    min-width: 0;
}
.topbar-logo { flex-shrink: 0; line-height: 0; }
.topbar-title {
    font-weight: 700;
    font-size: 1rem;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

/* Sidebar close button (mobile only) */
.sidebar-close {
    display: none;
    position: absolute;
    top: 0.6rem;
    right: 0.6rem;
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    color: var(--text);
    width: 36px;
    height: 36px;
    border-radius: var(--radius);
    cursor: pointer;
    align-items: center;
    justify-content: center;
    z-index: 2;
    transition: all var(--transition);
}
.sidebar-close:hover { border-color: var(--danger); color: var(--danger); }

/* Backdrop behind the sidebar overlay */
#sidebar-backdrop {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.55);
    backdrop-filter: blur(2px);
    z-index: 40;
    opacity: 0;
    transition: opacity var(--transition);
}
body.sidebar-open #sidebar-backdrop {
    display: block;
    opacity: 1;
}

/* ============================================
   RESPONSIVE — tablet and below: sidebar hides, slides in as overlay
   ============================================ */
@media (max-width: 880px) {
    body { overflow: auto; }

    #topbar { display: flex; }

    #app {
        grid-template-columns: 1fr;
        height: auto;
        min-height: calc(100vh - 56px);
    }

    #sidebar {
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        width: 280px;
        max-width: 85vw;
        z-index: 50;
        transform: translateX(-100%);
        transition: transform var(--transition);
        border-right: 1px solid var(--border);
        box-shadow: 4px 0 24px rgba(0, 0, 0, 0.4);
    }
    body.sidebar-open #sidebar {
        transform: translateX(0);
    }

    .sidebar-close { display: flex; }
    .brand { padding-right: 3rem; }   /* clear room for the close button */

    /* Calc layout stacks */
    .calc-layout {
        grid-template-columns: 1fr;
        max-width: none;
    }
    .side-panel { height: auto; }
    .panel-body { max-height: 280px; }

    #main {
        padding: 1rem 1rem 0;
        min-height: calc(100vh - 56px);
    }
    .app-tagline {
        font-size: 0.78rem;
        padding: 0.5rem 0.85rem;
        margin-bottom: 1rem;
    }
    .page-header { margin-bottom: 1rem; }
    .page-title { font-size: 1.4rem; }

    /* Tool cards a bit tighter */
    .tool-card { padding: 1rem; }

    /* Unit converter and currency stack vertically with bigger swap button */
    .unit-layout {
        grid-template-columns: 1fr;
        gap: 0.5rem;
    }
    .unit-swap {
        width: 100%;
        height: 44px;
        margin: 0;
        order: 2;
    }
    .unit-side:nth-of-type(1) { order: 1; }
    .unit-side:nth-of-type(3) { order: 3; }

    /* Equation form wraps cleanly */
    .eq-form { font-size: 1rem; gap: 0.4rem; }
    .eq-form .tool-input { width: 60px; }

    /* Matrix cells more thumb-friendly */
    .matrix-cell { width: 50px; height: 38px; font-size: 0.85rem; }
    .matrix-size { flex-wrap: wrap; }
    .matrix-size input { width: 50px; }

    /* Programmer bits readable */
    .prog-bits { gap: 0.2rem; }
    .prog-bit { padding: 0.5rem 0; font-size: 0.78rem; }
    .prog-bit-index { font-size: 0.55rem; }

    /* Graphing controls wrap */
    .graph-info { flex-direction: column; gap: 0.3rem; }
}

/* ============================================
   MOBILE — proper layout for narrow screens
   ============================================ */
@media (max-width: 640px) {
    #main { padding: 0.75rem 0.75rem 0; }

    .page-header { margin-bottom: 0.85rem; }
    .page-title { font-size: 1.2rem; }
    .page-subtitle { font-size: 0.85rem; }

    /* On the calc page specifically, the topbar already says "Scientific",
       so the page header just steals vertical space that the keypad needs.
       Hide subtitle and shrink title to claw back room. */
    body.is-calc .page-header { margin-bottom: 0.4rem; }
    body.is-calc .page-title { font-size: 1.05rem; margin-bottom: 0; }
    body.is-calc .page-subtitle { display: none; }
    body.is-calc .app-tagline { display: none; }

    /* Calculator container — tighter padding so keypad fits viewport */
    .calculator { padding: 0.6rem; }
    .display {
        padding: 0.55rem 0.75rem;
        min-height: auto;
        margin-bottom: 0.55rem;
    }
    .display-result { font-size: 1.55rem; }
    .display-expression { font-size: 0.78rem; min-height: 1.2em; }
    .display-meta { margin-bottom: 0.3rem; }

    /* Function keypad — 5 cols, smaller keys.
       This is 6 rows of scientific functions; if they're too tall the
       number pad falls below the fold. 38px each gives ~228px for the
       block, which fits on most phones above the number pad. */
    .keypad { gap: 0.35rem; }
    .keypad-fn {
        grid-template-columns: repeat(5, 1fr);
        gap: 0.28rem;
    }
    .keypad-fn .key {
        min-height: 38px;
        padding: 0.35rem 0.15rem;
        font-size: 0.78rem;
    }
    .keypad-fn .key.fn { font-size: 0.7rem; }
    .keypad-fn .key.mem { font-size: 0.7rem; }

    /* Number+ops get more room since they're the primary keys */
    .keypad-bottom {
        gap: 0.35rem;
        padding-top: 0.4rem;
    }
    .keypad-nums { gap: 0.35rem; }
    .keypad-ops { gap: 0.35rem; }
    .keypad-nums .key, .keypad-ops .key {
        min-height: 46px;
        padding: 0.55rem 0.15rem;
        font-size: 0.95rem;
    }
    .keypad-nums .key.num { font-size: 1.15rem; }
    .keypad-nums .key.fn { font-size: 0.78rem; }
    .keypad-nums .key.danger { font-size: 0.85rem; }
    .keypad-nums .key.mem { font-size: 0.78rem; }
    .keypad-ops .key.op { font-size: 1.25rem; }
    .keypad-ops .key.equals { font-size: 1.2rem; }

    /* Tool cards full width inputs */
    .tool-card { padding: 0.85rem; }
    .tool-card h3 { font-size: 0.72rem; margin-bottom: 0.6rem; }
    .tool-row { flex-direction: column; align-items: stretch; gap: 0.5rem; }
    .tool-row > .tool-label { min-width: 0; margin-bottom: 0; }
    .tool-input, .tool-select { width: 100%; font-size: 1rem; }
    .tool-btn { width: 100%; }

    /* Programmer ops wrap nicely */
    .prog-row { grid-template-columns: 50px 1fr; gap: 0.5rem; }
    .prog-base { font-size: 0.7rem; }
    .prog-value { font-size: 0.95rem; }

    /* Bits row: 4 cols on phone (so byte takes 2 rows but readable) */
    .prog-bits { grid-template-columns: repeat(8, 1fr); gap: 0.15rem; }
    .prog-bit { padding: 0.55rem 0; font-size: 0.75rem; }

    /* Stat tiles: 2 cols on phone */
    .stat-grid { grid-template-columns: repeat(2, 1fr); }

    /* Equation form: stack inputs and tokens */
    .eq-form {
        flex-direction: row;
        flex-wrap: wrap;
        justify-content: center;
        gap: 0.3rem;
        font-size: 0.95rem;
    }
    .eq-form .tool-input { width: 55px; padding: 0.45rem 0.4rem; }
    .eq-form .eq-token { font-size: 0.9rem; }

    /* Matrix scroll horizontally on overflow */
    .tool-card .matrix-grid {
        max-width: 100%;
        overflow-x: auto;
    }
    .matrix-cell { width: 44px; height: 36px; font-size: 0.8rem; }

    /* Tab strip wraps with smaller buttons */
    .tab-strip { gap: 0.3rem; }
    .tab-strip button { padding: 0.4rem 0.7rem; font-size: 0.8rem; }

    /* Side panel full width below calculator */
    .side-panel { gap: 0.75rem; }
    .panel-header { padding: 0.6rem 0.85rem; }
    .panel-header h2 { font-size: 0.72rem; }
    .panel-body { max-height: 220px; padding: 0.4rem; }
    .history-item { padding: 0.5rem 0.6rem; }
    .history-expr { font-size: 0.75rem; }
    .history-result { font-size: 0.9rem; }

    /* Topbar smaller on phone */
    #topbar { padding: 0.45rem 0.6rem; }
    .topbar-title { font-size: 0.95rem; }
    .topbar-btn { width: 38px; height: 38px; }

    /* Settings rows stack on phone */
    .setting-row {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
    }

    /* ============================================
       STANDARD MODE on mobile — extra polish.
       Without the function block above, the bottom
       keypad needs different proportions and the
       display meta row is more crowded by the toggle.
       ============================================ */
    .calc-layout.standard {
        grid-template-columns: 1fr;
    }
    /* The display meta row wraps with the toggle taking priority.
       DEG/RAD aren't visible in standard mode anyway. */
    .calc-layout.standard .display-meta {
        flex-wrap: wrap;
        row-gap: 6px;
    }
    /* Toggle pills get bigger touch targets on mobile */
    .mode-toggle .pill {
        padding: 0.3rem 0.85rem;
        font-size: 0.78rem;
    }
    /* Standard keypad: equal-ish split since ops column is only 5 keys.
       Make the keys taller to feel like a proper phone calculator. */
    .calc-layout.standard .keypad-bottom {
        grid-template-columns: 3.2fr 1fr;
        gap: 0.4rem;
    }
    .calc-layout.standard .keypad-nums { gap: 0.4rem; }
    .calc-layout.standard .keypad-ops { gap: 0.4rem; }
    .calc-layout.standard .key {
        min-height: 52px;
        padding: 0.7rem 0.2rem;
        font-size: 1rem;
    }
    .calc-layout.standard .key.num { font-size: 1.25rem; }
    .calc-layout.standard .key.op { font-size: 1.4rem; }
    .calc-layout.standard .key.equals { font-size: 1.3rem; }
    .calc-layout.standard .key.fn { font-size: 0.85rem; }
    .calc-layout.standard .key.mem { font-size: 0.85rem; }
    .calc-layout.standard .key.danger { font-size: 0.95rem; }

    /* Bigger result display in standard mode — it's the main attraction */
    .calc-layout.standard .display-result { font-size: 2rem; }
    .calc-layout.standard .display { min-height: 110px; }
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        transition-duration: 0.01ms !important;
        animation-duration: 0.01ms !important;
    }
}