/* Layout and design system: app shell, home page, calculators.
   style.css keeps the teaching-content components. Light theme only. */

:root {
    color-scheme: light;
    --teal-50: #f0fdfa;
    --teal-100: #ccfbf1;
    --teal-200: #99f6e4;
    --teal-600: #0d9488;
    --teal-700: #0f766e;
    --teal-800: #115e59;
    --sky-50: #f0f9ff;
    --sky-100: #e0f2fe;
    --sky-200: #bae6fd;
    --orange-50: #fff7ed;
    --orange-100: #ffedd5;
    --orange-500: #f97316;
    --orange-700: #c2410c;
    --orange-800: #9a3412;
    --ink-900: #0f172a;
    --ink-700: #334155;
    --ink-600: #475569;
    --ink-500: #64748b;
    --ink-300: #cbd5e1;
    --ink-200: #e2e8f0;
    --ink-100: #f1f5f9;
    --ink-50: #f8fafc;
    --danger-50: #fef2f2;
    --danger-600: #dc2626;
    --danger-700: #b91c1c;

    --font-ui: "Inter", "PingFang TC", "Noto Sans TC", "Microsoft JhengHei", system-ui, sans-serif;
    --font-code: "JetBrains Mono", "SFMono-Regular", Consolas, "PingFang TC", monospace;
    --radius-card: 16px;
    --radius-control: 10px;
    --shadow-card: 0 1px 2px rgba(15, 23, 42, 0.04), 0 8px 24px -12px rgba(15, 23, 42, 0.12);
    --shadow-raised: 0 12px 32px -12px rgba(15, 118, 110, 0.28);
    --nav-height: 56px;
}

/* ---------- Base ---------- */
*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    scroll-padding-top: calc(var(--nav-height) + 16px);
}

body {
    margin: 0;
    font-family: var(--font-ui);
    font-size: 16px;
    line-height: 1.65;
    color: var(--ink-700);
    background: var(--ink-50);
    -webkit-font-smoothing: antialiased;
}

img {
    max-width: 100%;
    height: auto;
}

:focus-visible {
    outline: 3px solid var(--orange-500);
    outline-offset: 2px;
}

.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
}

.skip-link {
    position: absolute;
    left: 16px;
    top: -60px;
    z-index: 1000;
    padding: 10px 16px;
    border-radius: var(--radius-control);
    background: var(--ink-900);
    color: #fff;
    text-decoration: none;
}

.skip-link:focus {
    top: 12px;
}

/* ---------- App header ---------- */
.app-header {
    background: #fff;
    border-bottom: 1px solid var(--ink-200);
}

.app-header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    min-height: 72px;
}

.brand {
    display: flex;
    align-items: center;
    gap: 12px;
    color: inherit;
    text-decoration: none;
}

.brand-mark {
    display: grid;
    place-items: center;
    width: 42px;
    height: 42px;
    border-radius: 12px;
    background: linear-gradient(135deg, var(--teal-600), var(--teal-800));
    color: #fff;
    font-size: 1.15rem;
    box-shadow: var(--shadow-raised);
}

.brand-title {
    margin: 0;
    font-size: 1.2rem;
    font-weight: 800;
    letter-spacing: -0.01em;
    color: var(--ink-900);
    line-height: 1.2;
}

.brand-subtitle {
    display: block;
    font-size: 0.82rem;
    color: var(--ink-500);
}

.maker {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    line-height: 1.3;
    text-decoration: none;
}

.maker-label {
    font-size: 0.75rem;
    color: var(--ink-500);
}

.maker-name {
    font-size: 0.92rem;
    font-weight: 700;
    color: var(--teal-700);
}

.maker:hover .maker-name {
    color: var(--orange-700);
}

/* ---------- Tab navigation ---------- */
.nav-tabs {
    position: sticky;
    top: 0;
    z-index: 50;
    background: rgba(255, 255, 255, 0.94);
    backdrop-filter: saturate(160%) blur(10px);
    border-bottom: 1px solid var(--ink-200);
}

.nav-inner {
    display: flex;
    align-items: center;
    gap: 4px;
    min-height: var(--nav-height);
    overflow-x: auto;
    scrollbar-width: none;
}

.nav-inner::-webkit-scrollbar {
    display: none;
}

.tab-group-label {
    flex: none;
    margin: 0 4px 0 16px;
    padding-left: 16px;
    border-left: 1px solid var(--ink-200);
    font-size: 0.72rem;
    font-weight: 700;
    letter-spacing: 0.08em;
    color: var(--ink-500);
    white-space: nowrap;
}

.tab-btn {
    position: relative;
    flex: none;
    display: inline-flex;
    align-items: center;
    gap: 8px;
    min-height: 40px;
    padding: 8px 14px;
    border: 0;
    border-radius: var(--radius-control);
    background: transparent;
    color: var(--ink-600);
    font: inherit;
    font-size: 0.92rem;
    font-weight: 600;
    white-space: nowrap;
    cursor: pointer;
    transition: background-color 0.15s, color 0.15s;
}

.tab-btn i {
    font-size: 0.9em;
    opacity: 0.8;
}

.tab-btn:hover {
    background: var(--ink-100);
    color: var(--ink-900);
}

.tab-btn.active {
    background: var(--teal-50);
    color: var(--teal-800);
}

.tab-btn.active::after {
    content: "";
    position: absolute;
    left: 14px;
    right: 14px;
    bottom: -8px;
    height: 3px;
    border-radius: 3px 3px 0 0;
    background: var(--orange-500);
}

/* ---------- Page shell ---------- */
.main-content {
    padding: 32px 0 72px;
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
    animation: tab-in 0.25s ease-out;
}

@keyframes tab-in {
    from { opacity: 0; transform: translateY(6px); }
    to { opacity: 1; transform: none; }
}

.module-header {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto;
    align-items: center;
    gap: 24px;
    margin-bottom: 24px;
    padding: 28px 32px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: linear-gradient(120deg, #fff 45%, var(--sky-50) 75%, var(--teal-50));
    box-shadow: var(--shadow-card);
}

.module-header h2 {
    margin: 0 0 6px;
    font-size: clamp(1.5rem, 2.4vw, 2rem);
    font-weight: 800;
    letter-spacing: -0.01em;
    color: var(--ink-900);
    line-height: 1.25;
}

.module-header p {
    margin: 0;
    max-width: 60ch;
    color: var(--ink-600);
}

.module-header-art {
    display: block;
    width: 200px;
    height: auto;
}

.module-header.is-banner .module-header-art {
    width: auto;
    max-width: 360px;
    max-height: 150px;
}

/* ---------- Buttons ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    min-height: 44px;
    padding: 10px 20px;
    border: 1px solid transparent;
    border-radius: var(--radius-control);
    font: inherit;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: background-color 0.15s, border-color 0.15s, transform 0.15s;
}

.btn:active {
    transform: translateY(1px);
}

.btn-accent {
    background: var(--orange-700);
    color: #fff;
}

.btn-accent:hover {
    background: var(--orange-800);
}

.btn-primary {
    background: var(--teal-700);
    color: #fff;
}

.btn-primary:hover {
    background: var(--teal-800);
}

.btn-ghost {
    background: #fff;
    border-color: var(--ink-300);
    color: var(--ink-700);
}

.btn-ghost:hover {
    border-color: var(--teal-600);
    color: var(--teal-800);
}

/* ---------- Home ---------- */
.home-hero {
    display: grid;
    grid-template-columns: minmax(0, 1.05fr) minmax(0, 1fr);
    align-items: center;
    gap: 32px;
    margin-bottom: 40px;
    padding: 40px;
    border: 1px solid var(--ink-200);
    border-radius: 24px;
    background:
        radial-gradient(circle at 85% 20%, var(--sky-100), transparent 55%),
        radial-gradient(circle at 70% 90%, var(--teal-50), transparent 50%),
        #fff;
    box-shadow: var(--shadow-card);
}

.eyebrow {
    margin: 0 0 12px;
    font-size: 0.8rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    color: var(--orange-700);
}

.home-hero h2 {
    margin: 0 0 16px;
    font-size: clamp(1.75rem, 3.4vw, 2.6rem);
    font-weight: 800;
    line-height: 1.25;
    letter-spacing: -0.02em;
    color: var(--ink-900);
}

.home-hero .lead {
    margin: 0 0 24px;
    font-size: 1.05rem;
    color: var(--ink-600);
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    margin-bottom: 24px;
}

.hero-points {
    display: flex;
    flex-wrap: wrap;
    gap: 8px 20px;
    margin: 0;
    padding: 0;
    list-style: none;
    font-size: 0.88rem;
    color: var(--ink-600);
}

.hero-points i {
    margin-right: 6px;
    color: var(--teal-600);
}

.home-hero-art img {
    display: block;
    width: 100%;
}

.guide-section {
    margin-bottom: 40px;
}

.guide-section > h3 {
    display: flex;
    align-items: center;
    gap: 10px;
    margin: 0 0 16px;
    font-size: 1.35rem;
    font-weight: 800;
    color: var(--ink-900);
}

.guide-section > h3 i {
    color: var(--teal-600);
}

.entry-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 20px;
}

.entry-card {
    display: flex;
    flex-direction: column;
    padding: 24px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
    box-shadow: var(--shadow-card);
    transition: transform 0.2s, box-shadow 0.2s, border-color 0.2s;
}

.entry-card:hover {
    transform: translateY(-3px);
    border-color: var(--teal-200);
    box-shadow: var(--shadow-raised);
}

.entry-card img {
    align-self: center;
    width: 180px;
    height: 140px;
    object-fit: contain;
    margin-bottom: 12px;
}

.entry-card h4 {
    margin: 0 0 6px;
    font-size: 1.15rem;
    color: var(--ink-900);
}

.entry-card > p {
    margin: 0 0 12px;
    color: var(--ink-600);
    font-size: 0.95rem;
}

.entry-tasks {
    flex: 1;
    margin: 0 0 20px;
    padding: 0;
    list-style: none;
}

.entry-tasks li {
    position: relative;
    padding: 4px 0 4px 20px;
    font-size: 0.92rem;
    color: var(--ink-700);
}

.entry-tasks li::before {
    content: "";
    position: absolute;
    left: 4px;
    top: 0.85em;
    width: 7px;
    height: 7px;
    border-radius: 50%;
    background: var(--orange-500);
}

.entry-card .btn {
    align-self: flex-start;
}

.guide-card {
    padding: 24px 28px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
    box-shadow: var(--shadow-card);
}

.guide-card h4 {
    margin: 0 0 12px;
    color: var(--teal-800);
}

.guide-steps {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 16px;
    margin: 0;
    padding: 0;
    list-style: none;
    counter-reset: step;
}

.guide-steps li {
    position: relative;
    padding: 44px 0 0;
    font-size: 0.93rem;
    color: var(--ink-600);
    counter-increment: step;
}

.guide-steps li::before {
    content: counter(step);
    position: absolute;
    top: 0;
    left: 0;
    display: grid;
    place-items: center;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    background: var(--teal-700);
    color: #fff;
    font-weight: 700;
}

.guide-steps strong {
    display: block;
    color: var(--ink-900);
}

.tips-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 20px;
}

.tip-card {
    padding: 22px 24px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
}

.tip-icon {
    display: grid;
    place-items: center;
    width: 40px;
    height: 40px;
    margin-bottom: 12px;
    border-radius: 10px;
    background: var(--teal-50);
    color: var(--teal-700);
    font-size: 1.1rem;
}

.tip-icon .fa-exclamation-triangle {
    color: var(--orange-700);
}

.tip-card:nth-child(2) .tip-icon {
    background: var(--orange-50);
}

.tip-card h4 {
    margin: 0 0 8px;
    font-size: 1.05rem;
    color: var(--ink-900);
}

.tip-card ul {
    margin: 0;
    padding-left: 1.1em;
    font-size: 0.92rem;
    color: var(--ink-600);
}

.tip-card li {
    margin-bottom: 4px;
}

/* Illustrations are drawn on white; multiply lets them sit on tinted panels. */
.home-hero-art img,
.module-header-art,
.entry-card img {
    mix-blend-mode: multiply;
}

/* ---------- Page table of contents ---------- */
.page-toc {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 8px;
    margin: 0 0 24px;
    padding: 14px 16px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
}

.page-toc-label {
    margin-right: 4px;
    font-size: 0.8rem;
    font-weight: 700;
    color: var(--ink-500);
}

.page-toc a {
    padding: 6px 12px;
    border-radius: 999px;
    background: var(--ink-100);
    color: var(--ink-700);
    font-size: 0.85rem;
    text-decoration: none;
    transition: background-color 0.15s, color 0.15s;
}

.page-toc a:hover {
    background: var(--teal-50);
    color: var(--teal-800);
}

/* ---------- "When to use" panels ---------- */
.usage-guide {
    margin-bottom: 24px;
    padding: 24px 28px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
}

.usage-header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 12px;
}

.usage-header h3 {
    margin: 0;
    font-size: 1.1rem;
    color: var(--ink-900);
}

.usage-header i {
    color: var(--teal-600);
}

.usage-content {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 24px;
}

.usage-content h4 {
    margin: 0 0 8px;
    font-size: 0.9rem;
    color: var(--ink-500);
}

.usage-content ul {
    margin: 0;
    padding-left: 1.2em;
}

.usage-content li {
    margin-bottom: 6px;
    font-size: 0.93rem;
}

.example-case {
    display: flex;
    align-items: baseline;
    gap: 10px;
    margin-bottom: 8px;
    padding: 10px 14px;
    border-radius: var(--radius-control);
    background: var(--ink-50);
    font-size: 0.9rem;
}

.example-tag {
    flex: none;
    padding: 2px 8px;
    border-radius: 6px;
    background: var(--teal-700);
    color: #fff;
    font-size: 0.75rem;
    font-weight: 700;
}

/* ---------- Calculators ---------- */
.calculator-grid {
    display: grid;
    gap: 24px;
}

.calculator-card {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    padding: 28px;
    border: 1px solid var(--ink-200);
    border-radius: var(--radius-card);
    background: #fff;
    box-shadow: var(--shadow-card);
    scroll-margin-top: calc(var(--nav-height) + 16px);
}

.calculator-card > h3 {
    display: flex;
    align-items: center;
    gap: 10px;
    margin: 0 0 20px;
    padding-bottom: 14px;
    border-bottom: 1px solid var(--ink-100);
    font-size: 1.2rem;
    font-weight: 800;
    color: var(--ink-900);
}

.calculator-card > h3 i {
    display: grid;
    place-items: center;
    width: 32px;
    height: 32px;
    border-radius: 9px;
    background: var(--teal-50);
    color: var(--teal-700);
    font-size: 0.85rem;
}

.input-group {
    margin-bottom: 14px;
}

.input-group label {
    display: block;
    margin-bottom: 6px;
    font-size: 0.86rem;
    font-weight: 600;
    color: var(--ink-700);
}

.input-group input[type="number"],
.input-group input[type="text"],
.input-group select {
    width: 100%;
    min-height: 44px;
    padding: 10px 12px;
    border: 1px solid var(--ink-300);
    border-radius: var(--radius-control);
    background: #fff;
    color: var(--ink-900);
    font: inherit;
    font-size: 0.95rem;
    transition: border-color 0.15s, box-shadow 0.15s;
}

.input-group input::placeholder {
    color: var(--ink-500);
    opacity: 0.8;
}

.input-group input:focus,
.input-group select:focus {
    outline: none;
    border-color: var(--teal-600);
    box-shadow: 0 0 0 3px var(--teal-100);
}

.input-group input[type="checkbox"] {
    width: 18px;
    height: 18px;
    margin-right: 8px;
    vertical-align: -3px;
    accent-color: var(--teal-700);
}

.input-hint {
    display: block;
    margin-top: 4px;
    font-size: 0.8rem;
    color: var(--ink-500);
}

/* Paired inputs (e.g. experimental vs control group) */
.field-row {
    margin: 0 0 6px;
    padding: 0;
    border: 0;
}

.field-row-title {
    display: flex;
    align-items: center;
    gap: 8px;
    margin: 0 0 8px;
    padding: 0;
    font-size: 0.8rem;
    font-weight: 700;
    letter-spacing: 0.04em;
    color: var(--teal-800);
}

.field-row-title::before {
    content: "";
    width: 8px;
    height: 8px;
    border-radius: 2px;
    background: var(--teal-600);
}

.field-row.is-control .field-row-title {
    color: var(--ink-600);
}

.field-row.is-control .field-row-title::before {
    background: var(--ink-500);
}

.field-row-fields {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(84px, 1fr));
    gap: 0 12px;
}

.calc-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    width: 100%;
    min-height: 48px;
    margin-top: 6px;
    border: 0;
    border-radius: var(--radius-control);
    background: var(--teal-700);
    color: #fff;
    font: inherit;
    font-weight: 700;
    cursor: pointer;
    transition: background-color 0.15s, transform 0.15s;
}

.calc-btn:hover {
    background: var(--teal-800);
}

.calc-btn:active {
    transform: translateY(1px);
}

.formula-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    min-height: 40px;
    margin-top: 12px;
    padding: 8px 14px;
    border: 1px dashed var(--ink-300);
    border-radius: var(--radius-control);
    background: transparent;
    color: var(--ink-600);
    font: inherit;
    font-size: 0.88rem;
    font-weight: 600;
    cursor: pointer;
    justify-self: start;
}

.formula-btn:hover {
    border-color: var(--teal-600);
    border-style: solid;
    color: var(--teal-800);
    background: var(--teal-50);
}

/* Result panel */
.result-box {
    position: relative;
    display: none;
    margin-top: 16px;
    padding: 18px 20px;
    border: 1px solid var(--teal-200);
    border-radius: 12px;
    background: var(--teal-50);
}

.result-box.has-result,
.result-box.has-error {
    display: block;
    animation: tab-in 0.2s ease-out;
}

.result-box.has-error {
    border-color: #fecaca;
    background: var(--danger-50);
}

.result-text {
    display: block;
    padding-right: 64px;
    font-family: var(--font-code);
    font-size: 0.86rem;
    line-height: 1.7;
    color: var(--ink-900);
    white-space: pre-wrap;
    word-break: break-word;
}

.result-box.has-error .result-text {
    padding-right: 0;
    font-family: var(--font-ui);
    color: var(--danger-700);
}

.result-box.has-error .copy-btn {
    display: none;
}

.copy-btn {
    position: absolute;
    top: 12px;
    right: 12px;
    min-height: 32px;
    padding: 4px 12px;
    border: 1px solid var(--teal-200);
    border-radius: 8px;
    background: #fff;
    color: var(--teal-800);
    font: inherit;
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
}

.copy-btn:hover {
    background: var(--teal-100);
}

.copy-status {
    display: block;
    margin-top: 6px;
    font-size: 0.8rem;
    color: var(--teal-800);
}

.copy-status:empty {
    display: none;
}

/* Wide cards: inputs on the left, result panel on the right. */
@media (min-width: 900px) {
    .calculator-card {
        grid-template-columns: minmax(0, 1fr) minmax(0, 1.1fr);
        /* The result panel spans every input row; its extra height goes to the final fr row. */
        grid-template-rows: auto repeat(18, auto) 1fr;
        column-gap: 32px;
    }

    .calculator-card > * {
        grid-column: 1;
    }

    .calculator-card > h3 {
        grid-column: 1 / -1;
    }

    .calculator-card > .result-box {
        grid-column: 2;
        grid-row: 2 / -1;
        align-self: start;
        display: block;
        position: sticky;
        top: calc(var(--nav-height) + 16px);
        margin-top: 0;
        min-height: 160px;
    }

    .calculator-card > .result-box:not(.has-result):not(.has-error) {
        border-style: dashed;
        border-color: var(--ink-300);
        background: var(--ink-50);
    }

    .calculator-card > .result-box:not(.has-result):not(.has-error)::before {
        content: "填入數值後按「計算」，結果與計算步驟會顯示在這裡。";
        display: block;
        color: var(--ink-500);
        font-size: 0.9rem;
    }

    .calculator-card > .result-box:not(.has-result):not(.has-error) .copy-btn {
        display: none;
    }
}

/* Inline notes inside calculators */
.note-box,
.es-usage-hint {
    margin-bottom: 16px;
    padding: 12px 14px;
    border-left: 3px solid var(--orange-500);
    border-radius: 0 var(--radius-control) var(--radius-control) 0;
    background: var(--orange-50);
    font-size: 0.88rem;
    color: var(--ink-700);
}

.note-box i,
.es-usage-hint i {
    color: var(--orange-700);
}

.es-usage-hint ul {
    margin: 6px 0 0;
    padding-left: 1.2em;
}

.es-usage-hint li {
    margin-bottom: 4px;
}

/* ---------- Formula modal ---------- */
.modal {
    display: none;
    position: fixed;
    inset: 0;
    z-index: 200;
    padding: 24px;
    overflow-y: auto;
    background: rgba(15, 23, 42, 0.5);
}

.modal-content {
    max-width: 720px;
    margin: 6vh auto;
    border-radius: var(--radius-card);
    background: #fff;
    box-shadow: 0 24px 64px -16px rgba(15, 23, 42, 0.45);
    animation: tab-in 0.2s ease-out;
}

.modal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    padding: 18px 24px;
    border-bottom: 1px solid var(--ink-200);
}

.modal-header h3 {
    margin: 0;
    font-size: 1.15rem;
    color: var(--ink-900);
}

.modal-close {
    display: grid;
    place-items: center;
    width: 40px;
    height: 40px;
    border: 0;
    border-radius: 10px;
    background: var(--ink-100);
    color: var(--ink-700);
    font-size: 1.4rem;
    cursor: pointer;
}

.modal-close:hover {
    background: var(--ink-200);
}

.modal-body {
    padding: 20px 24px 28px;
    font-size: 0.95rem;
}

.modal-body h4 {
    margin: 20px 0 8px;
    color: var(--teal-800);
}

.modal-body h4:first-child {
    margin-top: 0;
}

.modal-body p {
    margin: 0 0 8px;
}

.modal-body table td {
    padding: 6px 12px;
    border: 1px solid var(--ink-200);
}

/* ---------- Footer & back to top ---------- */
.footer {
    background: var(--ink-900);
    color: #cbd5e1;
    font-size: 0.88rem;
}

.footer-top {
    padding: 40px 0 28px;
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 32px;
}

.footer-heading {
    margin: 0 0 14px;
    font-size: 0.85rem;
    font-weight: 700;
    color: #f1f5f9;
}

.footer-column ul {
    margin: 0;
    padding: 0;
    list-style: none;
}

.footer-column li {
    margin-bottom: 12px;
}

.footer a {
    color: var(--teal-200);
    text-underline-offset: 3px;
}

.footer a:hover {
    color: #fff;
}

.footer-follow-list {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
}

.footer-follow-list li {
    margin: 0;
}

.footer-follow-list a {
    display: grid;
    place-items: center;
    width: 46px;
    height: 46px;
    border: 1px solid rgba(255, 255, 255, 0.12);
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.04);
    color: #e2e8f0;
    transition: background-color 0.15s, color 0.15s, border-color 0.15s;
}

.footer-follow-list a:hover {
    border-color: var(--teal-200);
    background: var(--teal-800);
    color: #fff;
}

.footer-follow-list svg {
    width: 22px;
    height: 22px;
}

.footer-about {
    margin-top: 28px;
    color: #94a3b8;
}

.footer p {
    font-size: inherit;
}

.footer-about p,
.footer-bottom p {
    margin: 0 0 6px;
    color: #94a3b8;
}

.footer-bottom {
    padding: 20px 0 28px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    color: #94a3b8;
}

.footer-bottom-inner {
    display: flex;
    justify-content: space-between;
    gap: 24px;
}

.footer-bottom-inner p:last-child {
    max-width: 60ch;
    text-align: right;
}

.back-to-top {
    position: fixed;
    right: 20px;
    bottom: 20px;
    z-index: 60;
    display: grid;
    place-items: center;
    width: 48px;
    height: 48px;
    border: 0;
    border-radius: 50%;
    background: var(--teal-700);
    color: #fff;
    box-shadow: var(--shadow-raised);
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transform: translateY(8px);
    transition: opacity 0.2s, transform 0.2s, visibility 0.2s;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: none;
}

/* ---------- Responsive ---------- */
@media (max-width: 1024px) {
    .footer-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .footer-grid .footer-column:last-child {
        grid-column: 1 / -1;
    }

    .home-hero {
        grid-template-columns: minmax(0, 1fr);
        padding: 32px;
    }

    .home-hero-art {
        order: -1;
        max-width: 520px;
        margin: 0 auto;
    }

    .entry-grid {
        grid-template-columns: minmax(0, 1fr);
    }

    .tips-grid {
        grid-template-columns: minmax(0, 1fr);
    }

    .entry-card {
        display: grid;
        grid-template-columns: 140px minmax(0, 1fr);
        column-gap: 20px;
    }

    .entry-card img {
        grid-row: 1 / span 4;
        width: 140px;
        height: 120px;
    }

    .module-header.is-banner .module-header-art {
        max-width: 260px;
    }
}

@media (max-width: 720px) {
    .container {
        padding: 0 16px;
    }

    .app-header-inner {
        min-height: 60px;
    }

    .brand-mark {
        width: 36px;
        height: 36px;
    }

    .brand-title {
        font-size: 1.05rem;
    }

    .brand-subtitle {
        font-size: 0.75rem;
    }

    .nav-tabs {
        /* Hint that the tab row scrolls horizontally. */
        -webkit-mask-image: linear-gradient(90deg, #000 88%, transparent);
        mask-image: linear-gradient(90deg, #000 88%, transparent);
    }

    .tab-group-label {
        display: none;
    }

    .tab-btn {
        padding: 8px 12px;
        font-size: 0.88rem;
    }

    .main-content {
        padding-top: 20px;
    }

    .home-hero {
        padding: 24px 20px;
        border-radius: 18px;
    }

    .hero-actions .btn {
        flex: 1 1 100%;
    }

    .entry-card {
        grid-template-columns: minmax(0, 1fr);
    }

    .entry-card img {
        grid-row: auto;
        width: 150px;
        height: 110px;
    }

    .module-header {
        grid-template-columns: minmax(0, 1fr);
        padding: 22px 20px;
    }

    .module-header-art,
    .module-header.is-banner .module-header-art {
        display: none;
    }

    .page-toc {
        flex-wrap: nowrap;
        overflow-x: auto;
        scrollbar-width: none;
        -webkit-mask-image: linear-gradient(90deg, #000 85%, transparent);
        mask-image: linear-gradient(90deg, #000 85%, transparent);
    }

    .page-toc::-webkit-scrollbar {
        display: none;
    }

    .page-toc a,
    .page-toc-label {
        flex: none;
        white-space: nowrap;
    }

    .usage-guide {
        padding: 20px;
    }

    .usage-content {
        grid-template-columns: minmax(0, 1fr);
        gap: 12px;
    }

    .calculator-card {
        padding: 20px;
    }

    .guide-card {
        padding: 20px;
    }

    .modal {
        padding: 12px;
    }

    .maker {
        display: none;
    }

    .footer-grid {
        grid-template-columns: minmax(0, 1fr);
    }

    .footer-bottom-inner {
        flex-direction: column;
        gap: 4px;
    }

    .footer-bottom-inner p:last-child {
        text-align: left;
    }

    .modal-content {
        margin: 2vh auto;
    }
}

@media (prefers-reduced-motion: reduce) {
    html {
        scroll-behavior: auto;
    }

    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        transition-duration: 0.01ms !important;
    }
}

@media print {
    .app-header,
    .nav-tabs,
    .page-toc,
    .back-to-top,
    .calc-btn,
    .formula-btn,
    .copy-btn {
        display: none !important;
    }

    body {
        background: #fff;
    }

    .calculator-card,
    .module-header {
        box-shadow: none;
        break-inside: avoid;
    }
}