/* ============================================
   快手 App 下载 - 完整样式
   配色：快手红 + 渐变紫橙 + 亮白
   ============================================ */

/* ---------- CSS Variables ---------- */
:root {
    --primary: #FF4D4D;
    --primary-dark: #E63939;
    --primary-light: #FF7777;
    --secondary: #FF7A00;
    --gradient-main: linear-gradient(135deg, #FF4D4D, #FF7A00);
    --gradient-text: linear-gradient(135deg, #FF4D4D, #FF9A44);
    --bg-dark: #0D0D0D;
    --bg-card: #1A1A2E;
    --bg-section: #111128;
    --bg-light: #F8F9FA;
    --text-primary: #FFFFFF;
    --text-secondary: #B0B0C3;
    --text-muted: #6C6C80;
    --border-color: rgba(255, 255, 255, 0.08);
    --shadow-sm: 0 4px 20px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 8px 40px rgba(255, 77, 77, 0.15);
    --shadow-lg: 0 16px 60px rgba(255, 77, 77, 0.25);
    --radius-sm: 12px;
    --radius-md: 20px;
    --radius-lg: 28px;
    --radius-full: 50%;
    --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --max-width: 1200px;
}

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

html {
    scroll-behavior: smooth;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font);
    background-color: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
}

img {
    max-width: 100%;
    display: block;
}

a {
    text-decoration: none;
    color: inherit;
}

ul {
    list-style: none;
}

.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 24px;
}

/* ---------- Typography ---------- */
.gradient-text {
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.section-header {
    text-align: center;
    margin-bottom: 56px;
}

.section-header h2 {
    font-size: 2.4rem;
    font-weight: 700;
    margin-bottom: 12px;
    letter-spacing: -0.5px;
}

.section-header p {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* ---------- Buttons ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    padding: 14px 32px;
    border-radius: 50px;
    font-weight: 600;
    font-size: 1rem;
    line-height: 1;
    border: none;
    cursor: pointer;
    transition: var(--transition);
    text-align: center;
}

.btn i {
    font-size: 1.1em;
}

.btn-primary {
    background: var(--gradient-main);
    color: #fff;
    box-shadow: 0 4px 20px rgba(255, 77, 77, 0.35);
}

.btn-primary:hover {
    transform: translateY(-3px) scale(1.02);
    box-shadow: 0 8px 30px rgba(255, 77, 77, 0.45);
}

.btn-primary:active {
    transform: translateY(-1px) scale(0.98);
}

.btn-outline {
    background: transparent;
    color: var(--text-primary);
    border: 2px solid rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
}

.btn-outline:hover {
    border-color: var(--primary);
    background: rgba(255, 77, 77, 0.1);
    transform: translateY(-2px);
}

.btn-large {
    padding: 16px 36px;
    font-size: 1.05rem;
}

/* ---------- Header ---------- */
.site-header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    padding: 16px 0;
    transition: var(--transition);
    background: transparent;
}

.site-header.scrolled {
    background: rgba(13, 13, 13, 0.85);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    box-shadow: 0 2px 30px rgba(0, 0, 0, 0.5);
    padding: 10px 0;
    border-bottom: 1px solid var(--border-color);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 1.5rem;
    font-weight: 700;
}

.logo-icon {
    color: var(--primary);
    font-size: 1.6rem;
}

.logo-text {
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.main-nav ul {
    display: flex;
    gap: 8px;
}

.main-nav ul li a {
    padding: 8px 18px;
    border-radius: 50px;
    font-weight: 500;
    color: var(--text-secondary);
    transition: var(--transition);
    position: relative;
    font-size: 0.95rem;
}

.main-nav ul li a:hover,
.main-nav ul li a.active {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.06);
}

.mobile-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 1.6rem;
    cursor: pointer;
    padding: 4px;
}

.mobile-close {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 1.5rem;
    cursor: pointer;
    position: absolute;
    top: 20px;
    right: 24px;
}

/* ---------- Hero ---------- */
.hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    align-items: center;
    padding: 120px 0 80px;
    overflow: hidden;
}

.hero-bg-decor {
    position: absolute;
    top: -30%;
    right: -15%;
    width: 700px;
    height: 700px;
    background: radial-gradient(circle, rgba(255, 77, 77, 0.12) 0%, transparent 70%);
    border-radius: 50%;
    pointer-events: none;
    z-index: 0;
}

.hero-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 60px;
    align-items: center;
    position: relative;
    z-index: 1;
}

.hero-text h1 {
    font-size: 3.8rem;
    font-weight: 800;
    line-height: 1.15;
    letter-spacing: -1px;
    margin-bottom: 20px;
}

.hero-subtitle {
    font-size: 1.15rem;
    color: var(--text-secondary);
    margin-bottom: 36px;
    max-width: 480px;
    line-height: 1.7;
}

.hero-stats {
    display: flex;
    gap: 40px;
    margin-bottom: 40px;
}

.stat-item {
    display: flex;
    flex-direction: column;
}

.stat-number {
    font-size: 1.8rem;
    font-weight: 700;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-top: 2px;
}

.hero-buttons {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
}

/* ---------- Phone Mockup ---------- */
.hero-mockup {
    display: flex;
    justify-content: center;
    align-items: center;
}

.phone-frame {
    width: 280px;
    height: 580px;
    background: #1a1a1a;
    border-radius: 40px;
    padding: 12px;
    box-shadow: 0 30px 80px rgba(0, 0, 0, 0.6), inset 0 0 0 2px rgba(255, 255, 255, 0.05);
    position: relative;
}

.phone-screen {
    width: 100%;
    height: 100%;
    background: #0a0a0a;
    border-radius: 32px;
    overflow: hidden;
    display: flex;
    flex-direction: column;
    position: relative;
}

.mockup-video {
    flex: 1;
    background: linear-gradient(45deg, #2a0845, #6441A5, #ff6a00);
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
}

.play-icon {
    font-size: 3rem;
    color: rgba(255, 255, 255, 0.8);
    filter: drop-shadow(0 0 20px rgba(255, 77, 77, 0.5));
    z-index: 2;
}

.mockup-overlay {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 50%;
    background: linear-gradient(transparent, rgba(0,0,0,0.7));
}

.mockup-toolbar {
    display: flex;
    align-items: center;
    justify-content: space-around;
    padding: 12px 16px;
    background: rgba(0,0,0,0.6);
    color: #fff;
    font-size: 0.8rem;
}

.mockup-toolbar span i {
    margin-right: 4px;
}

.mockup-heart i { color: #ff4d4d; }
.mockup-comment i { color: #fff; }
.mockup-share i { color: #fff; }

.mockup-user {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 12px 16px;
    background: rgba(0,0,0,0.7);
    border-top: 1px solid rgba(255,255,255,0.05);
}

.mockup-avatar {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    object-fit: cover;
    border: 2px solid var(--primary);
}

.mockup-username {
    font-size: 0.85rem;
    color: #ddd;
}

/* ---------- Features ---------- */
.features {
    padding: 100px 0;
    background: var(--bg-section);
}

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

.feature-card {
    background: var(--bg-card);
    border-radius: var(--radius-md);
    padding: 36px 28px;
    text-align: center;
    border: 1px solid var(--border-color);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 3px;
    background: var(--gradient-main);
    opacity: 0;
    transition: var(--transition);
}

.feature-card:hover {
    transform: translateY(-6px);
    box-shadow: var(--shadow-md);
    border-color: rgba(255, 77, 77, 0.2);
}

.feature-card:hover::before {
    opacity: 1;
}

.feature-icon {
    width: 64px;
    height: 64px;
    border-radius: var(--radius-sm);
    background: rgba(255, 77, 77, 0.1);
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 20px;
    font-size: 1.6rem;
    color: var(--primary);
    transition: var(--transition);
}

.feature-card:hover .feature-icon {
    background: var(--gradient-main);
    color: #fff;
    transform: scale(1.1);
}

.feature-card h3 {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 10px;
}

.feature-card p {
    color: var(--text-secondary);
    font-size: 0.95rem;
    line-height: 1.6;
}

/* ---------- Download ---------- */
.download {
    padding: 100px 0;
    position: relative;
}

.download-card {
    background: var(--bg-card);
    border-radius: var(--radius-lg);
    padding: 48px;
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 48px;
    align-items: center;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-sm);
}

.download-info h2 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 8px;
}

.download-version {
    color: var(--text-muted);
    font-size: 0.95rem;
    margin-bottom: 20px;
}

.download-desc {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 28px;
}

.download-desc li {
    display: flex;
    align-items: center;
    gap: 10px;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.download-desc li i {
    color: var(--primary);
}

.download-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 14px;
    margin-bottom: 20px;
}

.download-note {
    color: var(--text-muted);
    font-size: 0.9rem;
}

.download-note i {
    color: var(--primary);
    margin-right: 6px;
}

.download-qr {
    display: flex;
    align-items: center;
    justify-content: center;
}

.qr-box {
    text-align: center;
    background: #fff;
    border-radius: var(--radius-sm);
    padding: 24px;
    box-shadow: 0 8px 30px rgba(0,0,0,0.3);
}

.qr-code {
    width: 150px;
    height: 150px;
    margin: 0 auto 12px;
}

.qr-code img {
    width: 100%;
    height: 100%;
    object-fit: contain;
}

.qr-box p {
    color: #333;
    font-weight: 600;
    font-size: 0.95rem;
}

/* ---------- FAQ ---------- */
.faq {
    padding: 100px 0;
    background: var(--bg-section);
}

.faq-list {
    max-width: 720px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.faq-item {
    background: var(--bg-card);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-color);
    overflow: hidden;
    transition: var(--transition);
}

.faq-item:hover {
    border-color: rgba(255, 77, 77, 0.2);
}

.faq-question {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 24px;
    cursor: pointer;
    font-weight: 600;
    font-size: 1rem;
    user-select: none;
    transition: var(--transition);
}

.faq-question i {
    transition: var(--transition);
    color: var(--text-muted);
    font-size: 0.9rem;
}

.faq-item.active .faq-question i {
    transform: rotate(180deg);
    color: var(--primary);
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s ease, padding 0.4s ease;
    padding: 0 24px;
}

.faq-item.active .faq-answer {
    max-height: 300px;
    padding: 0 24px 20px;
}

.faq-answer p {
    color: var(--text-secondary);
    line-height: 1.7;
    font-size: 0.95rem;
}

/* ---------- Footer ---------- */
.site-footer {
    background: #0a0a0a;
    padding: 60px 0 30px;
    border-top: 1px solid var(--border-color);
}

.footer-content {
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: 48px;
    margin-bottom: 40px;
}

.footer-brand .logo {
    margin-bottom: 16px;
}

.footer-brand p {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 20px;
    max-width: 280px;
}

.footer-social {
    display: flex;
    gap: 12px;
}

.footer-social a {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.05);
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-secondary);
    transition: var(--transition);
    font-size: 1.1rem;
}

.footer-social a:hover {
    background: var(--gradient-main);
    color: #fff;
    transform: translateY(-2px);
}

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

.footer-col h4 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 16px;
    color: var(--text-primary);
}

.footer-col ul li {
    margin-bottom: 10px;
}

.footer-col ul li a {
    color: var(--text-secondary);
    font-size: 0.9rem;
    transition: var(--transition);
}

.footer-col ul li a:hover {
    color: var(--primary);
}

.footer-bottom {
    border-top: 1px solid var(--border-color);
    padding-top: 24px;
    text-align: center;
}

.footer-bottom p {
    color: var(--text-muted);
    font-size: 0.85rem;
}

/* ---------- Back to Top ---------- */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 48px;
    height: 48px;
    background: var(--gradient-main);
    color: #fff;
    border: none;
    border-radius: 50%;
    font-size: 1.2rem;
    cursor: pointer;
    box-shadow: var(--shadow-md);
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: var(--transition);
    z-index: 999;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:hover {
    transform: translateY(-3px) scale(1.05);
    box-shadow: var(--shadow-lg);
}

/* ---------- Toast ---------- */
.toast {
    position: fixed;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%) translateY(80px);
    background: rgba(0, 0, 0, 0.85);
    backdrop-filter: blur(12px);
    color: #fff;
    padding: 14px 28px;
    border-radius: 50px;
    font-size: 0.95rem;
    font-weight: 500;
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.5);
    border: 1px solid rgba(255, 255, 255, 0.08);
    z-index: 9999;
    opacity: 0;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    pointer-events: none;
}

.toast.show {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
}

/* ---------- Responsive ---------- */
@media (max-width: 1024px) {
    .hero-grid {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-subtitle {
        margin: 0 auto 36px;
    }

    .hero-stats {
        justify-content: center;
    }

    .hero-buttons {
        justify-content: center;
    }

    .hero-mockup {
        order: -1;
    }

    .phone-frame {
        width: 220px;
        height: 460px;
    }

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

    .download-card {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .download-desc {
        align-items: center;
    }

    .download-buttons {
        justify-content: center;
    }

    .download-qr {
        margin-top: 20px;
    }

    .footer-content {
        grid-template-columns: 1fr;
    }

    .footer-links {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (max-width: 768px) {
    .container {
        padding: 0 16px;
    }

    .main-nav {
        position: fixed;
        top: 0;
        right: -100%;
        width: 280px;
        height: 100vh;
        background: rgba(13, 13, 13, 0.98);
        backdrop-filter: blur(20px);
        padding: 80px 30px 40px;
        transition: right 0.4s cubic-bezier(0.4, 0, 0.2, 1);
        z-index: 1001;
        border-left: 1px solid var(--border-color);
    }

    .main-nav.open {
        right: 0;
    }

    .main-nav ul {
        flex-direction: column;
        gap: 4px;
    }

    .main-nav ul li a {
        font-size: 1.1rem;
        padding: 12px 16px;
        display: block;
    }

    .mobile-toggle {
        display: block;
    }

    .mobile-close {
        display: block;
    }

    .hero-text h1 {
        font-size: 2.4rem;
    }

    .hero-stats {
        gap: 24px;
    }

    .stat-number {
        font-size: 1.4rem;
    }

    .section-header h2 {
        font-size: 1.8rem;
    }

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

    .download-card {
        padding: 32px 20px;
    }

    .download-info h2 {
        font-size: 1.6rem;
    }

    .download-buttons .btn {
        width: 100%;
    }

    .footer-links {
        grid-template-columns: 1fr 1fr;
    }

    .back-to-top {
        bottom: 20px;
        right: 20px;
        width: 40px;
        height: 40px;
        font-size: 1rem;
    }
}

@media (max-width: 480px) {
    .phone-frame {
        width: 180px;
        height: 380px;
        border-radius: 28px;
        padding: 8px;
    }

    .phone-screen {
        border-radius: 22px;
    }

    .hero-text h1 {
        font-size: 2rem;
    }

    .hero-buttons .btn {
        width: 100%;
        justify-content: center;
    }

    .footer-links {
        grid-template-columns: 1fr;
    }

    .toast {
        width: calc(100% - 32px);
        text-align: center;
    }
}