/* ============================================
   快手 App 下载 - 完整样式
   配色：快手红 + 渐变紫橙 + 亮白
   包含：管理后台样式
   ============================================ */

/* ---------- CSS Variables ---------- */
:root {
    --primary: #fe2c55;
    --primary-dark: #d91a3e;
    --secondary: #ff6b35;
    --accent: #ffd700;
    --bg-dark: #0f0f0f;
    --bg-card: #1a1a2e;
    --text-primary: #ffffff;
    --text-secondary: #b0b0b0;
    --gradient-main: linear-gradient(135deg, #fe2c55, #ff6b35);
    --gradient-hero: linear-gradient(135deg, #0f0f0f 0%, #1a1a2e 50%, #2a1a3e 100%);
    --shadow-card: 0 8px 32px rgba(254, 44, 85, 0.15);
    --border-radius: 16px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'PingFang SC', 'Microsoft YaHei', sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
}

a {
    text-decoration: none;
    color: inherit;
    transition: var(--transition);
}

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

ul {
    list-style: none;
}

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

/* ---------- Buttons ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 14px 32px;
    border-radius: 50px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    border: none;
    transition: var(--transition);
    text-align: center;
    justify-content: center;
}

.btn-primary {
    background: var(--gradient-main);
    color: #fff;
    box-shadow: 0 4px 20px rgba(254, 44, 85, 0.4);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 30px rgba(254, 44, 85, 0.6);
}

.btn-outline {
    background: transparent;
    color: var(--text-primary);
    border: 2px solid rgba(255,255,255,0.3);
}

.btn-outline:hover {
    border-color: var(--primary);
    background: rgba(254, 44, 85, 0.1);
}

/* ---------- Header ---------- */
.site-header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    padding: 12px 0;
    transition: var(--transition);
    background: transparent;
}

.site-header.scrolled {
    background: rgba(15, 15, 15, 0.95);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    box-shadow: 0 2px 20px rgba(0,0,0,0.3);
    padding: 8px 0;
}

.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: 800;
    color: var(--text-primary);
}

.logo i {
    font-size: 1.8rem;
    background: var(--gradient-main);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.main-nav ul {
    display: flex;
    gap: 32px;
}

.main-nav a {
    font-size: 0.95rem;
    color: var(--text-secondary);
    padding: 6px 0;
    position: relative;
    font-weight: 500;
}

.main-nav a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--gradient-main);
    transition: var(--transition);
    border-radius: 2px;
}

.main-nav a:hover,
.main-nav a.active {
    color: var(--text-primary);
}

.main-nav a:hover::after,
.main-nav a.active::after {
    width: 100%;
}

.admin-link {
    display: flex;
    align-items: center;
    gap: 4px;
    color: var(--secondary) !important;
}

.admin-link i {
    font-size: 0.85rem;
}

/* ---------- Menu Toggle ---------- */
.menu-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 4px;
}

.menu-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: var(--transition);
}

.menu-toggle.active span:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}
.menu-toggle.active span:nth-child(2) {
    opacity: 0;
}
.menu-toggle.active span:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

/* ---------- Hero Section ---------- */
.hero-section {
    min-height: 100vh;
    display: flex;
    align-items: center;
    position: relative;
    overflow: hidden;
    padding: 100px 0 60px;
    background: var(--gradient-hero);
}

.hero-bg {
    position: absolute;
    top: -50%;
    right: -20%;
    width: 800px;
    height: 800px;
    background: radial-gradient(circle, rgba(254,44,85,0.15) 0%, transparent 70%);
    border-radius: 50%;
    pointer-events: none;
}

.hero-content {
    display: flex;
    align-items: center;
    gap: 60px;
    position: relative;
    z-index: 1;
}

.hero-text {
    flex: 1;
}

.hero-text h1 {
    font-size: 3.5rem;
    font-weight: 900;
    line-height: 1.2;
    background: var(--gradient-main);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 16px;
}

.hero-subtitle {
    font-size: 1.2rem;
    color: var(--text-secondary);
    margin-bottom: 24px;
}

.hero-badges {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    margin-bottom: 32px;
}

.badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 6px 16px;
    background: rgba(255,255,255,0.08);
    border-radius: 50px;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.badge i {
    color: var(--primary);
}

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

.hero-visual {
    flex: 1;
    display: flex;
    justify-content: center;
}

.phone-mockup {
    width: 280px;
    height: 560px;
    background: #1a1a2e;
    border-radius: 40px;
    padding: 12px;
    box-shadow: 0 20px 60px rgba(0,0,0,0.5), inset 0 0 0 1px rgba(255,255,255,0.1);
    position: relative;
}

.phone-screen {
    width: 100%;
    height: 100%;
    border-radius: 32px;
    overflow: hidden;
    background: #111;
    padding: 16px 12px;
}

.screen-content {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.video-card {
    background: rgba(255,255,255,0.05);
    border-radius: 12px;
    overflow: hidden;
    animation: float 3s ease-in-out infinite;
    animation-delay: calc(var(--i) * 0.3s);
}

.video-thumb {
    height: 80px;
    border-radius: 12px 12px 0 0;
}

.video-info {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 12px;
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.avatar {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    display: block;
}

@keyframes float {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-6px); }
}

.scroll-indicator {
    position: absolute;
    bottom: 24px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 6px;
    color: var(--text-secondary);
    font-size: 0.8rem;
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateX(-50%) translateY(0); }
    50% { transform: translateX(-50%) translateY(8px); }
}

/* ---------- Section Header ---------- */
.section-header {
    text-align: center;
    margin-bottom: 48px;
}

.section-header h2 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: 12px;
    background: var(--gradient-main);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

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

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

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

.feature-card {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 32px 24px;
    text-align: center;
    transition: var(--transition);
    border: 1px solid rgba(255,255,255,0.05);
}

.feature-card:hover {
    transform: translateY(-6px);
    box-shadow: var(--shadow-card);
    border-color: rgba(254,44,85,0.2);
}

.feature-icon {
    width: 64px;
    height: 64px;
    margin: 0 auto 20px;
    background: rgba(254,44,85,0.1);
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.6rem;
    color: var(--primary);
    transition: var(--transition);
}

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

.feature-card h3 {
    font-size: 1.2rem;
    margin-bottom: 12px;
    font-weight: 700;
}

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

/* ---------- Download Section ---------- */
.download-section {
    padding: 100px 0;
    background: linear-gradient(135deg, #0f0f0f, #1a1a2e);
}

.download-options {
    display: flex;
    gap: 24px;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 40px;
}

.download-card {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 20px 28px;
    background: var(--bg-card);
    border-radius: var(--border-radius);
    border: 1px solid rgba(255,255,255,0.08);
    transition: var(--transition);
    min-width: 280px;
    cursor: pointer;
}

.download-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-card);
    border-color: var(--primary);
}

.download-icon {
    font-size: 2.2rem;
    width: 56px;
    height: 56px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(255,255,255,0.05);
    border-radius: 12px;
}

.download-card.ios .download-icon { color: #999; }
.download-card.android .download-icon { color: #3ddc84; }

.download-info {
    flex: 1;
    display: flex;
    flex-direction: column;
}

.download-label {
    font-size: 1rem;
    font-weight: 600;
}

.download-version {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.download-btn {
    padding: 8px 20px;
    background: var(--gradient-main);
    border-radius: 50px;
    font-size: 0.85rem;
    font-weight: 600;
    transition: var(--transition);
}

.download-card:hover .download-btn {
    transform: scale(1.05);
}

.download-note {
    text-align: center;
    color: var(--text-secondary);
}

.download-note p {
    margin-bottom: 12px;
}

.qrcode-placeholder {
    width: 120px;
    height: 120px;
    margin: 0 auto;
    background: rgba(255,255,255,0.05);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 3rem;
    color: var(--text-secondary);
    border: 2px dashed rgba(255,255,255,0.1);
}

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

.faq-list {
    max-width: 700px;
    margin: 0 auto;
}

.faq-item {
    background: var(--bg-card);
    border-radius: 12px;
    margin-bottom: 12px;
    overflow: hidden;
    border: 1px solid rgba(255,255,255,0.05);
    transition: var(--transition);
}

.faq-item:hover {
    border-color: rgba(254,44,85,0.15);
}

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

.faq-question i {
    transition: var(--transition);
    color: var(--text-secondary);
}

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

.faq-answer {
    max-height: 0;
    padding: 0 24px;
    overflow: hidden;
    transition: var(--transition);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.faq-item.active .faq-answer {
    max-height: 200px;
    padding: 0 24px 20px;
}

/* ---------- Footer ---------- */
.site-footer {
    padding: 40px 0;
    background: #0a0a0a;
    border-top: 1px solid rgba(255,255,255,0.05);
}

.footer-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 16px;
    text-align: center;
}

.footer-brand {
    font-size: 1.2rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: 8px;
}

.footer-brand i {
    color: var(--primary);
}

.footer-links {
    display: flex;
    gap: 24px;
    flex-wrap: wrap;
    justify-content: center;
}

.footer-links a {
    color: var(--text-secondary);
    font-size: 0.85rem;
}

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

.footer-copyright {
    color: var(--text-secondary);
    font-size: 0.8rem;
}

/* ---------- Back to Top ---------- */
.back-to-top {
    position: fixed;
    bottom: 80px;
    right: 24px;
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background: var(--gradient-main);
    color: #fff;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    box-shadow: 0 4px 20px rgba(254,44,85,0.4);
    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(-4px);
    box-shadow: 0 8px 30px rgba(254,44,85,0.6);
}

/* ========== 管理后台样式 ========== */

/* 浮动入口按钮 */
.admin-float-btn {
    position: fixed;
    bottom: 24px;
    right: 24px;
    width: 52px;
    height: 52px;
    border-radius: 50%;
    background: var(--gradient-main);
    color: #fff;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
    box-shadow: 0 4px 20px rgba(254,44,85,0.5);
    z-index: 998;
    transition: var(--transition);
    animation: pulse-shadow 2s infinite;
}

.admin-float-btn:hover {
    transform: scale(1.1) rotate(30deg);
    box-shadow: 0 8px 30px rgba(254,44,85,0.7);
}

@keyframes pulse-shadow {
    0%, 100% { box-shadow: 0 4px 20px rgba(254,44,85,0.4); }
    50% { box-shadow: 0 4px 30px rgba(254,44,85,0.7); }
}

/* 模态框 */
.admin-modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 9999;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
}

.admin-modal.open {
    opacity: 1;
    visibility: visible;
}

.admin-modal-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.7);
    backdrop-filter: blur(4px);
    -webkit-backdrop-filter: blur(4px);
}

.admin-modal-content {
    position: relative;
    width: 90%;
    max-width: 560px;
    max-height: 80vh;
    background: var(--bg-card);
    border-radius: 20px;
    border: 1px solid rgba(255,255,255,0.1);
    box-shadow: 0 20px 60px rgba(0,0,0,0.5);
    overflow: hidden;
    transform: scale(0.9) translateY(20px);
    transition: var(--transition);
}

.admin-modal.open .admin-modal-content {
    transform: scale(1) translateY(0);
}

.admin-modal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 20px 28px;
    border-bottom: 1px solid rgba(255,255,255,0.08);
}

.admin-modal-header h2 {
    font-size: 1.2rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: 8px;
}

.admin-modal-header h2 i {
    color: var(--primary);
}

.admin-modal-close {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 1.6rem;
    cursor: pointer;
    transition: var(--transition);
    line-height: 1;
}

.admin-modal-close:hover {
    color: var(--primary);
    transform: rotate(90deg);
}

.admin-modal-body {
    padding: 28px;
    overflow-y: auto;
    max-height: calc(80vh - 80px);
}

/* 登录表单 */
.admin-login-form {
    display: none;
    flex-direction: column;
    gap: 20px;
}

.admin-login-form.active {
    display: flex;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.form-group label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.form-group input {
    padding: 12px 16px;
    background: rgba(255,255,255,0.05);
    border: 1px solid rgba(255,255,255,0.1);
    border-radius: 10px;
    color: var(--text-primary);
    font-size: 0.95rem;
    outline: none;
    transition: var(--transition);
}

.form-group input:focus {
    border-color: var(--primary);
    background: rgba(254,44,85,0.05);
    box-shadow: 0 0 0 3px rgba(254,44,85,0.1);
}

.form-group input::placeholder {
    color: var(--text-secondary);
    opacity: 0.6;
}

.admin-login-btn {
    width: 100%;
    margin-top: 8px;
}

.admin-login-error {
    color: var(--primary);
    font-size: 0.85rem;
    text-align: center;
    min-height: 20px;
}

/* 管理面板 */
.admin-panel {
    display: none;
    flex-direction: column;
    gap: 20px;
}

.admin-panel.active {
    display: flex;
}

.admin-panel-tabs {
    display: flex;
    gap: 8px;
    border-bottom: 1px solid rgba(255,255,255,0.08);
    padding-bottom: 12px;
}

.tab-btn {
    padding: 8px 16px;
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    border-radius: 8px;
    transition: var(--transition);
}

.tab-btn.active {
    background: rgba(254,44,85,0.15);
    color: var(--primary);
}

.tab-btn:hover:not(.active) {
    background: rgba(255,255,255,0.05);
}

.tab-content {
    display: none;
    flex-direction: column;
    gap: 16px;
}

.tab-content.active {
    display: flex;
}

.tab-content h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-secondary);
}

/* 数据卡片 */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
}

.stat-card {
    background: rgba(255,255,255,0.03);
    border-radius: 12px;
    padding: 20px 16px;
    text-align: center;
    border: 1px solid rgba(255,255,255,0.05);
}

.stat-value {
    display: block;
    font-size: 1.8rem;
    font-weight: 800;
    background: var(--gradient-main);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 4px;
}

.stat-label {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

/* 下载日志表格 */
.download-log table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.85rem;
}

.download-log th,
.download-log td {
    padding: 8px 12px;
    text-align: left;
    border-bottom: 1px solid rgba(255,255,255,0.05);
}

.download-log th {
    color: var(--text-secondary);
    font-weight: 600;
    font-size: 0.8rem;
}

.download-log td {
    color: var(--text-primary);
}

.download-log tbody tr:hover {
    background: rgba(255,255,255,0.03);
}

/* 设置表单 */
.settings-form {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.settings-form .form-group input {
    width: 100%;
}

.save-feedback {
    font-size: 0.85rem;
    color: #4caf50;
    min-height: 20px;
}

.logout-btn {
    margin-top: 8px;
    align-self: flex-start;
}

/* ---------- Responsive ---------- */
@media (max-width: 992px) {
    .hero-content {
        flex-direction: column;
        text-align: center;
    }
    .hero-text h1 {
        font-size: 2.5rem;
    }
    .hero-badges {
        justify-content: center;
    }
    .hero-actions {
        justify-content: center;
    }
    .features-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    .phone-mockup {
        width: 220px;
        height: 440px;
    }
}

@media (max-width: 768px) {
    .menu-toggle {
        display: flex;
    }
    .main-nav {
        position: fixed;
        top: 60px;
        left: 0;
        width: 100%;
        background: rgba(15, 15, 15, 0.98);
        backdrop-filter: blur(20px);
        -webkit-backdrop-filter: blur(20px);
        padding: 20px 24px;
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: var(--transition);
        border-bottom: 1px solid rgba(255,255,255,0.05);
    }
    .main-nav.open {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }
    .main-nav ul {
        flex-direction: column;
        gap: 16px;
    }
    .main-nav a {
        font-size: 1.1rem;
    }
    .hero-text h1 {
        font-size: 2rem;
    }
    .section-header h2 {
        font-size: 1.8rem;
    }
    .features-grid {
        grid-template-columns: 1fr;
    }
    .download-card {
        min-width: 100%;
    }
    .stats-grid {
        grid-template-columns: 1fr;
    }
    .admin-modal-content {
        max-width: 95%;
    }
    .admin-modal-body {
        padding: 20px;
    }
    .admin-panel-tabs {
        flex-wrap: wrap;
    }
}

@media (max-width: 480px) {
    .hero-text h1 {
        font-size: 1.6rem;
    }
    .btn {
        padding: 12px 24px;
        font-size: 0.9rem;
    }
    .phone-mockup {
        width: 180px;
        height: 360px;
    }
    .admin-float-btn {
        width: 44px;
        height: 44px;
        font-size: 1.2rem;
        bottom: 16px;
        right: 16px;
    }
    .back-to-top {
        bottom: 70px;
        right: 16px;
        width: 40px;
        height: 40px;
        font-size: 1rem;
    }
}

【特色】分类：下载站；架构：纯静态；本次修改：添加管理后台功能；修改文件：index.html, script.js, style.css；主要变化：新增管理后台模态框，包含登录、数据概览、下载日志、系统设置等功能，增加浮动入口按钮和导航管理链接，完善后台交互逻辑。