/* ===========================================
   What Changed - Demo Page Styles
   =========================================== */

/* CSS Variables */
:root {
    --color-primary: #1976d2;
    --color-primary-dark: #1565c0;
    --color-deleted-bg: #ffebee;
    --color-deleted-fg: #b71c1c;
    --color-added-bg: #e8f5e9;
    --color-added-fg: #1b5e20;
    --color-text: #263238;
    --color-text-light: #546e7a;
    --color-bg: #fafafa;
    --color-white: #ffffff;
    --color-separator: #cfd8dc;
    --font-serif: 'Noto Serif SC', 'Georgia', serif;
    --font-sans: 'Inter', 'Segoe UI', sans-serif;
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
}

/* Reset & Base */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    color: var(--color-text);
    background: var(--color-bg);
    line-height: 1.6;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px;
}

/* Typography */
h1,
h2,
h3 {
    font-family: var(--font-serif);
    font-weight: 700;
    line-height: 1.3;
}

a {
    color: var(--color-primary);
    text-decoration: none;
    transition: color 0.2s ease;
}

a:hover {
    color: var(--color-primary-dark);
}

/* ===========================================
   Language Switcher
   =========================================== */
.lang-switcher {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 1000;
}

.lang-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    background: rgba(255, 255, 255, 0.95);
    border: none;
    padding: 10px 16px;
    border-radius: 50px;
    cursor: pointer;
    font-size: 14px;
    font-weight: 600;
    color: var(--color-text);
    box-shadow: var(--shadow-md);
    transition: all 0.3s ease;
    backdrop-filter: blur(10px);
}

.lang-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.lang-icon {
    font-size: 18px;
}

.lang-arrow {
    font-size: 10px;
    opacity: 0.6;
    transition: transform 0.2s ease;
}

.lang-dropdown {
    position: absolute;
    top: 100%;
    right: 0;
    margin-top: 8px;
    background: var(--color-white);
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-lg);
    overflow: hidden;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-10px);
    transition: all 0.2s ease;
    min-width: 120px;
}

.lang-dropdown.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.lang-option {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px 16px;
    cursor: pointer;
    transition: background 0.2s ease;
    font-size: 14px;
}

.lang-option:hover {
    background: var(--color-bg);
}

.lang-check {
    width: 16px;
    color: var(--color-primary);
    font-weight: bold;
}

/* Fade-in animation */
.fade-in {
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in.visible {
    opacity: 1;
    transform: translateY(0);
}

/* Demo text visibility - controlled by JS */
.demo-text-en,
.demo-text-zh {
    display: none;
}

/* ===========================================
   Hero Section
   =========================================== */
.hero {
    background: linear-gradient(135deg, #1976d2 0%, #2196f3 50%, #42a5f5 100%);
    color: var(--color-white);
    padding: 80px 0;
    text-align: center;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 700;
    margin-bottom: 12px;
    letter-spacing: -1px;
}

.hero-subtitle {
    font-size: 1.5rem;
    font-weight: 400;
    opacity: 0.95;
    margin-bottom: 8px;
}

.hero-tagline {
    font-size: 1.1rem;
    opacity: 0.85;
    margin-bottom: 32px;
    letter-spacing: 2px;
}

/* Buttons */
.btn-primary {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    background: var(--color-white);
    color: var(--color-primary);
    font-weight: 600;
    font-size: 1rem;
    padding: 14px 28px;
    border-radius: 50px;
    box-shadow: var(--shadow-md);
    transition: all 0.3s ease;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
    color: var(--color-primary-dark);
}

.btn-large {
    font-size: 1.1rem;
    padding: 16px 32px;
}

.btn-icon {
    font-size: 1.2rem;
}

/* ===========================================
   Sections
   =========================================== */
.section {
    padding: 80px 0;
}

.section-title {
    font-size: 2.2rem;
    text-align: center;
    margin-bottom: 16px;
    color: var(--color-text);
}

.section-title em {
    color: var(--color-deleted-fg);
    font-style: normal;
}

.section-desc {
    text-align: center;
    color: var(--color-text-light);
    font-size: 1.1rem;
    margin-bottom: 48px;
}

/* ===========================================
   Why Section
   =========================================== */
.why-section {
    background: var(--color-white);
}

.problem-solution {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 32px;
}

.problem-card,
.solution-card {
    padding: 32px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
}

.problem-card {
    background: #fff8f8;
    border-left: 4px solid var(--color-deleted-fg);
}

.solution-card {
    background: #f8fff8;
    border-left: 4px solid var(--color-added-fg);
}

.problem-card h3,
.solution-card h3 {
    font-size: 1.3rem;
    margin-bottom: 16px;
}

.problem-card ul,
.solution-card ul {
    list-style: none;
}

.problem-card li,
.solution-card li {
    padding: 8px 0;
    padding-left: 24px;
    position: relative;
}

.problem-card li::before {
    content: "•";
    position: absolute;
    left: 0;
    color: var(--color-deleted-fg);
}

.solution-card li::before {
    content: "✓";
    position: absolute;
    left: 0;
    color: var(--color-added-fg);
}

/* ===========================================
   Demo Section
   =========================================== */
.demo-section {
    background: var(--color-bg);
}

.demo-container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
    margin-bottom: 24px;
}

.demo-panel {
    background: var(--color-white);
    border-radius: var(--radius-md);
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

.panel-header {
    padding: 12px 20px;
    font-weight: 600;
    font-size: 0.9rem;
}

.original-panel .panel-header {
    background: var(--color-deleted-bg);
    color: var(--color-deleted-fg);
}

.revised-panel .panel-header {
    background: var(--color-added-bg);
    color: var(--color-added-fg);
}

.panel-content {
    padding: 20px;
    font-family: var(--font-serif);
    font-size: 0.95rem;
    line-height: 1.8;
    min-height: 280px;
}

.diff-block {
    margin-bottom: 16px;
}

.diff-header {
    display: inline-block;
    font-family: var(--font-sans);
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--color-text-light);
    margin-bottom: 8px;
}

.deleted-header {
    color: var(--color-deleted-fg);
}

.added-header {
    color: var(--color-added-fg);
}

.deleted {
    background: var(--color-deleted-bg);
    color: var(--color-deleted-fg);
    text-decoration: line-through;
    padding: 2px 4px;
    border-radius: 3px;
}

.added {
    background: var(--color-added-bg);
    color: var(--color-added-fg);
    padding: 2px 4px;
    border-radius: 3px;
}

.deleted-block {
    background: var(--color-deleted-bg);
    color: var(--color-deleted-fg);
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    margin-bottom: 8px;
}

.added-block {
    background: var(--color-added-bg);
    color: var(--color-added-fg);
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    margin-bottom: 8px;
}

.separator {
    height: 1px;
    background: var(--color-separator);
    margin: 20px 0;
}

.demo-note {
    text-align: center;
    color: var(--color-text-light);
    font-size: 0.95rem;
    background: var(--color-white);
    padding: 16px 24px;
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-sm);
}

/* ===========================================
   Examples Section
   =========================================== */
.examples-section {
    background: var(--color-white);
}

.examples-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.example-card {
    padding: 28px;
    background: var(--color-bg);
    border-radius: var(--radius-md);
    text-align: center;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.example-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.example-card h3 {
    font-size: 1.2rem;
    margin-bottom: 12px;
}

.example-card p {
    color: var(--color-text-light);
    font-size: 0.95rem;
}

/* ===========================================
   Features Section
   =========================================== */
.features-section {
    background: var(--color-bg);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.feature-card {
    background: var(--color-white);
    padding: 32px;
    border-radius: var(--radius-md);
    text-align: center;
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.feature-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.feature-icon {
    font-size: 2.5rem;
    display: block;
    margin-bottom: 16px;
}

.feature-card h3 {
    font-size: 1.15rem;
    margin-bottom: 8px;
}

.feature-card p {
    color: var(--color-text-light);
    font-size: 0.9rem;
}

/* ===========================================
   Not For Section
   =========================================== */
.not-for-section {
    background: var(--color-white);
}

.not-for-list {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 16px;
    margin-bottom: 48px;
}

.not-for-item {
    background: #f5f5f5;
    padding: 12px 20px;
    border-radius: 50px;
    font-size: 0.95rem;
    color: var(--color-text-light);
}

.philosophy-quote {
    text-align: center;
    font-family: var(--font-serif);
    font-size: 1.3rem;
    font-style: italic;
    color: var(--color-text-light);
    max-width: 600px;
    margin: 0 auto;
    padding: 24px;
    border-left: 4px solid var(--color-primary);
    background: var(--color-bg);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

/* ===========================================
   Download Section
   =========================================== */
.download-section {
    background: linear-gradient(135deg, #1976d2 0%, #2196f3 100%);
    color: var(--color-white);
    text-align: center;
}

.download-section .section-title {
    color: var(--color-white);
}

.download-section .section-desc {
    color: rgba(255, 255, 255, 0.9);
}

.download-buttons {
    margin-bottom: 24px;
}

.download-note {
    font-size: 0.9rem;
    opacity: 0.8;
}

/* ===========================================
   Footer
   =========================================== */
.footer {
    background: #263238;
    color: #90a4ae;
    padding: 40px 0;
    text-align: center;
}

.footer a {
    color: #90a4ae;
    padding: 0 8px;
}

.footer a:hover {
    color: var(--color-white);
}

.copyright {
    margin-top: 12px;
    font-size: 0.85rem;
    opacity: 0.7;
}

/* ===========================================
   Responsive Design
   =========================================== */
@media (max-width: 900px) {

    .problem-solution,
    .demo-container {
        grid-template-columns: 1fr;
    }

    .features-grid,
    .examples-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 600px) {
    .hero-title {
        font-size: 2.5rem;
    }

    .hero-subtitle {
        font-size: 1.2rem;
    }

    .section-title {
        font-size: 1.8rem;
    }

    .features-grid,
    .examples-grid {
        grid-template-columns: 1fr;
    }

    .not-for-list {
        flex-direction: column;
        align-items: center;
    }

    .lang-switcher {
        top: 10px;
        right: 10px;
    }

    .lang-btn {
        padding: 8px 12px;
        font-size: 12px;
    }
}