/* ============================================
   爱途伴旅官网 — 极简黑白风
   参考: Linear.app, Apple, Vercel
   ============================================ */

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

:root {
    /* Color System — 严格黑白灰 */
    --color-black: #000000;
    --color-white: #FFFFFF;
    --color-gray-50: #FAFAFA;
    --color-gray-100: #F5F5F5;
    --color-gray-200: #E5E5E5;
    --color-gray-300: #D4D4D4;
    --color-gray-400: #A3A3A3;
    --color-gray-500: #737373;
    --color-gray-600: #525252;
    --color-gray-700: #404040;
    --color-gray-800: #262626;
    --color-gray-900: #171717;

    /* Typography */
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;

    /* Spacing Scale */
    --space-1: 4px;
    --space-2: 8px;
    --space-3: 12px;
    --space-4: 16px;
    --space-5: 20px;
    --space-6: 24px;
    --space-8: 32px;
    --space-10: 40px;
    --space-12: 48px;
    --space-16: 64px;
    --space-20: 80px;
    --space-24: 96px;
    --space-32: 128px;

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 400ms ease;
}

html {
    scroll-behavior: smooth;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-sans);
    font-size: 18px;
    line-height: 1.6;
    color: var(--color-black);
    background: var(--color-white);
    overflow-x: hidden;
}

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

/* ============================================
   Layout
   ============================================ */

.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-6);
}

@media (min-width: 768px) {
    .container {
        padding: 0 var(--space-10);
    }
}

@media (min-width: 1400px) {
    .container {
        max-width: 1320px;
    }
}

/* ============================================
   Logo Icon
   ============================================ */

.logo-icon {
    width: 32px;
    height: 32px;
    border-radius: 8px;
    object-fit: cover;
    flex-shrink: 0;
}

/* ============================================
   Navigation
   ============================================ */

.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    transition: background var(--transition-base), backdrop-filter var(--transition-base);
}

.nav-scrolled {
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(20px) saturate(180%);
    -webkit-backdrop-filter: blur(20px) saturate(180%);
}

.nav-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    position: relative;
    height: 72px;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-6);
}

@media (min-width: 768px) {
    .nav-inner {
        padding: 0 var(--space-10);
    }
}

@media (min-width: 1400px) {
    .nav-inner {
        max-width: 1320px;
    }
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-weight: 600;
    font-size: 20px;
    letter-spacing: -0.01em;
}

.nav-links {
    display: none;
    align-items: center;
    gap: var(--space-8);
}

@media (min-width: 640px) {
    .nav-links {
        display: flex;
    }
}

.nav-link {
    font-size: 16px;
    font-weight: 500;
    color: var(--color-gray-600);
    transition: color var(--transition-fast);
    letter-spacing: -0.01em;
}

.nav-link:hover {
    color: var(--color-black);
}

.nav-logo {
    height: 64px;
    display: flex;
    align-items: center;
}

.nav-logo img {
    height: 100%;
    width: auto;
    display: block;
}

.nav-logo-text {
    font-size: 26px;
    font-weight: 900;
    color: var(--color-black);
    margin-left: var(--space-3);
    letter-spacing: -0.01em;
    white-space: nowrap;
}

/* ============================================
   Buttons
   ============================================ */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-2);
    font-family: inherit;
    font-size: 15px;
    font-weight: 500;
    letter-spacing: -0.01em;
    border: none;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-small {
    height: 40px;
    padding: 0 var(--space-6);
    background: var(--color-black);
    color: var(--color-white);
    border-radius: 10px;
}

.btn-small:hover {
    background: var(--color-gray-800);
    transform: translateY(-1px);
}

.btn-primary {
    height: 56px;
    padding: 0 var(--space-10);
    background: var(--color-black);
    color: var(--color-white);
    border-radius: 14px;
    font-size: 17px;
    font-weight: 600;
}

.btn-primary:hover {
    background: var(--color-gray-800);
    transform: translateY(-2px);
}

.btn-primary svg {
    transition: transform var(--transition-fast);
}

.btn-primary:hover svg {
    transform: translateX(3px);
}

/* ============================================
   Hero
   ============================================ */

.hero {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    position: relative;
    padding: var(--space-24) var(--space-6) var(--space-20);
    text-align: center;
}

.hero-content {
    max-width: 780px;
}

.hero-label {
    font-size: 15px;
    font-weight: 500;
    color: var(--color-gray-400);
    letter-spacing: 0.08em;
    text-transform: uppercase;
    margin-bottom: var(--space-8);
}

.hero-title {
    font-size: clamp(44px, 8vw, 80px);
    font-weight: 700;
    line-height: 1.08;
    letter-spacing: -0.03em;
    margin-bottom: var(--space-6);
}

.hero-subtitle {
    font-size: clamp(18px, 2.5vw, 22px);
    font-weight: 400;
    color: var(--color-gray-500);
    line-height: 1.7;
    margin-bottom: var(--space-10);
    letter-spacing: -0.01em;
}

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

/* Scroll Indicator */
.scroll-indicator {
    position: absolute;
    bottom: var(--space-10);
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--space-2);
}

.scroll-line {
    width: 1px;
    height: 40px;
    background: linear-gradient(to bottom, var(--color-gray-300), transparent);
    animation: scrollPulse 2s ease-in-out infinite;
}

@keyframes scrollPulse {
    0%, 100% {
        opacity: 0.4;
        transform: scaleY(0.7);
        transform-origin: top;
    }
    50% {
        opacity: 1;
        transform: scaleY(1);
        transform-origin: top;
    }
}

/* ============================================
   Section Header
   ============================================ */

.section-header {
    margin-bottom: var(--space-16);
}

.section-number {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    border: 1px solid var(--color-gray-200);
    border-radius: 10px;
    font-size: 13px;
    font-weight: 600;
    color: var(--color-gray-500);
    background: var(--color-white);
    letter-spacing: 0;
    margin-bottom: var(--space-5);
    transition: all var(--transition-base);
}

.section-header:hover .section-number {
    background: var(--color-black);
    border-color: var(--color-black);
    color: var(--color-white);
    transform: translateY(-2px);
}

.section-title {
    font-size: clamp(32px, 4vw, 44px);
    font-weight: 700;
    letter-spacing: -0.02em;
    line-height: 1.2;
    margin-bottom: var(--space-4);
}

.section-desc {
    font-size: 19px;
    color: var(--color-gray-500);
    font-weight: 400;
    letter-spacing: -0.01em;
}

/* ============================================
   Service
   ============================================ */

.service {
    padding: var(--space-32) 0;
    background: var(--color-white);
}

.service-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--space-6);
}

@media (min-width: 768px) {
    .service-grid {
        grid-template-columns: repeat(3, 1fr);
        gap: var(--space-8);
    }
}

.service-card {
    padding: var(--space-8);
    border: 1px solid var(--color-gray-200);
    border-radius: 16px;
    transition: all var(--transition-base);
}

.service-card:hover {
    border-color: var(--color-gray-400);
    transform: translateY(-4px);
    box-shadow: 0 20px 40px -20px rgba(0, 0, 0, 0.08);
}

.service-icon {
    width: 60px;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--color-gray-200);
    border-radius: 14px;
    margin-bottom: var(--space-6);
    color: var(--color-black);
    transition: all var(--transition-base);
}

.service-card:hover .service-icon {
    background: var(--color-black);
    border-color: var(--color-black);
    color: var(--color-white);
}

.service-name {
    font-size: 22px;
    font-weight: 600;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-3);
}

.service-desc {
    font-size: 17px;
    color: var(--color-gray-500);
    line-height: 1.7;
    letter-spacing: -0.01em;
}

/* ============================================
   Divider
   ============================================ */

.divider {
    height: 1px;
    background: var(--color-gray-200);
    max-width: 1200px;
    margin: 0 auto;
}

@media (min-width: 1400px) {
    .divider {
        max-width: 1320px;
    }
}

/* ============================================
   Features
   ============================================ */

.features {
    padding: var(--space-32) 0;
    background: var(--color-gray-50);
}

.feature-list {
    display: flex;
    flex-direction: column;
    gap: 0;
}

.feature-item {
    display: flex;
    gap: var(--space-8);
    padding: var(--space-10) 0;
    border-bottom: 1px solid var(--color-gray-200);
}

.feature-item:last-child {
    border-bottom: none;
}

.feature-number {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    border: 1px solid var(--color-gray-100);
    border-radius: 8px;
    font-size: 11px;
    font-weight: 600;
    color: var(--color-gray-400);
    background: var(--color-white);
    flex-shrink: 0;
    transition: all var(--transition-base);
}

.feature-item:hover .feature-number {
    border-color: var(--color-gray-300);
    color: var(--color-black);
}

.feature-content h3 {
    font-size: clamp(22px, 3vw, 30px);
    font-weight: 600;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-3);
}

.feature-content p {
    font-size: 18px;
    color: var(--color-gray-500);
    line-height: 1.7;
    max-width: 520px;
}

@media (min-width: 768px) {
    .feature-item {
        padding: var(--space-12) 0;
        gap: var(--space-16);
    }
}

/* ============================================
   Download
   ============================================ */

.download {
    padding: var(--space-32) 0;
    background: var(--color-white);
}

.download-inner {
    text-align: center;
    max-width: 680px;
    margin: 0 auto;
}

.download-title {
    font-size: clamp(32px, 4vw, 44px);
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-4);
}

.download-desc {
    font-size: 19px;
    color: var(--color-gray-500);
    margin-bottom: var(--space-12);
    letter-spacing: -0.01em;
}

.download-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-8);
}

.download-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--space-4);
}

.qr-placeholder {
    width: 120px;
    height: 120px;
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px dashed var(--color-gray-300);
    border-radius: 12px;
    color: var(--color-gray-400);
    transition: all var(--transition-base);
}

.qr-placeholder:hover {
    border-color: var(--color-gray-500);
    color: var(--color-gray-600);
}

.download-label {
    font-size: 17px;
    font-weight: 600;
    letter-spacing: -0.01em;
}

.download-note {
    font-size: 15px;
    color: var(--color-gray-400);
    font-weight: 400;
}

@media (min-width: 768px) {
    .qr-placeholder {
        width: 160px;
        height: 160px;
    }
}

@media (min-width: 1024px) {
    .qr-placeholder {
        width: 180px;
        height: 180px;
    }
}

/* ============================================
   Footer
   ============================================ */

.footer {
    padding: var(--space-20) 0 var(--space-10);
    background: var(--color-black);
    color: var(--color-white);
}

.footer-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--space-12);
    margin-bottom: var(--space-16);
}

@media (min-width: 768px) {
    .footer-grid {
        grid-template-columns: 1fr 1fr;
        gap: var(--space-16);
    }
}

.footer-brand {
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-size: 20px;
    font-weight: 600;
    letter-spacing: -0.01em;
}

.footer-tagline {
    font-size: 17px;
    color: var(--color-gray-500);
    font-weight: 400;
}

.footer-info {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--space-8);
}

.footer-group {
    display: flex;
    flex-direction: column;
    gap: var(--space-2);
}

.footer-label {
    font-size: 14px;
    font-weight: 500;
    color: var(--color-gray-600);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-group p,
.footer-group a {
    font-size: 16px;
    color: var(--color-gray-400);
    font-weight: 400;
    transition: color var(--transition-fast);
}

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

.footer-bottom {
    padding-top: var(--space-8);
    border-top: 1px solid var(--color-gray-800);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--space-3);
    text-align: center;
}

.icp {
    font-size: 14px;
    color: var(--color-gray-600);
}

.copyright {
    font-size: 14px;
    color: var(--color-gray-700);
}

/* ============================================
   Responsive — Mobile / Tablet / Desktop
   ============================================ */

/* Mobile: < 640px */
@media (max-width: 639px) {
    .download-grid {
        grid-template-columns: 1fr;
        gap: var(--space-10);
    }

    .qr-placeholder {
        width: 160px;
        height: 160px;
    }

    .feature-item {
        flex-direction: column;
        gap: var(--space-4);
    }

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

/* Tablet: 640px - 1023px */
@media (min-width: 640px) and (max-width: 1023px) {
    .hero-title {
        font-size: 56px;
    }

    .section-title {
        font-size: 36px;
    }

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

    .service-card:last-child {
        grid-column: 1 / -1;
        max-width: 50%;
        margin: 0 auto;
    }
}

/* Desktop: >= 1024px */
@media (min-width: 1024px) {
    .nav-inner {
        height: 80px;
    }

    .hero {
        padding-top: var(--space-24);
    }

    .service-card {
        padding: var(--space-10);
    }

    .feature-item {
        padding: var(--space-16) 0;
    }
}

/* Large Desktop: >= 1400px */
@media (min-width: 1400px) {
    .hero-title {
        font-size: 88px;
    }

    .service-grid {
        gap: var(--space-10);
    }
}

/* ============================================
   Animation Utilities
   ============================================ */

@media (prefers-reduced-motion: no-preference) {
    .service-card,
    .feature-item {
        opacity: 0;
        transform: translateY(20px);
        animation: fadeUp 0.6s ease forwards;
    }

    .service-card:nth-child(1) { animation-delay: 0.1s; }
    .service-card:nth-child(2) { animation-delay: 0.2s; }
    .service-card:nth-child(3) { animation-delay: 0.3s; }

    .feature-item:nth-child(1) { animation-delay: 0.1s; }
    .feature-item:nth-child(2) { animation-delay: 0.2s; }
    .feature-item:nth-child(3) { animation-delay: 0.3s; }
}

@keyframes fadeUp {
    to {
        opacity: 1;
        transform: translateY(0);
    }
}