/* ============================================
   张老成个人网站 - 简约专业风格
   ============================================ */

/* CSS Variables */
:root {
    /* Colors */
    --color-primary: #1a1a1a;
    --color-secondary: #666666;
    --color-muted: #999999;
    --color-light: #f5f5f5;
    --color-white: #ffffff;
    --color-border: #e0e0e0;
    --color-accent: #2563eb;
    --color-accent-hover: #1d4ed8;

    /* AI Direction */
    --color-ai: #8b5cf6;
    --color-ai-bg: #f5f3ff;

    /* Low Altitude Direction */
    --color-low: #0ea5e9;
    --color-low-bg: #f0f9ff;

    /* Business Direction */
    --color-biz: #f59e0b;
    --color-biz-bg: #fffbeb;

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;

    /* Typography */
    --font-sans: 'Inter', 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-serif: 'Noto Sans SC', serif;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    font-size: 16px;
    line-height: 1.7;
    color: var(--color-primary);
    background: var(--color-white);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* ============================================
   Navigation
   ============================================ */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--color-border);
    z-index: 1000;
}

.navbar .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 70px;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.nav-brand a {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-primary);
    text-decoration: none;
}

.nav-tag {
    font-size: 0.75rem;
    padding: 0.25rem 0.75rem;
    background: var(--color-light);
    color: var(--color-secondary);
    border-radius: var(--radius-lg);
    font-weight: 500;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-lg);
}

.nav-menu a {
    font-size: 0.9375rem;
    color: var(--color-secondary);
    text-decoration: none;
    transition: color 0.2s ease;
    position: relative;
}

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

.nav-menu a.active::after {
    content: '';
    position: absolute;
    bottom: -24px;
    left: 0;
    right: 0;
    height: 2px;
    background: var(--color-accent);
}

.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    cursor: pointer;
}

.nav-toggle span {
    width: 24px;
    height: 2px;
    background: var(--color-primary);
    transition: all 0.3s ease;
}

/* ============================================
   Hero Section
   ============================================ */
.hero {
    padding: calc(70px + var(--spacing-2xl)) 0 var(--spacing-2xl);
    background: linear-gradient(135deg, #fafafa 0%, #f5f5f5 100%);
}

.hero-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-2xl);
    align-items: center;
}

.hero-text {
    max-width: 600px;
}

.hero-subtitle {
    font-size: 1rem;
    color: var(--color-accent);
    font-weight: 500;
    margin-bottom: var(--spacing-sm);
    letter-spacing: 0.05em;
}

.hero h1 {
    font-size: 3rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
    color: var(--color-primary);
}

.hero-description {
    font-size: 1.125rem;
    color: var(--color-secondary);
    line-height: 1.8;
    margin-bottom: var(--spacing-lg);
}

.hero-description strong {
    color: var(--color-primary);
    font-weight: 600;
}

.hero-actions {
    display: flex;
    gap: var(--spacing-sm);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.875rem 1.75rem;
    font-size: 1rem;
    font-weight: 500;
    border-radius: var(--radius-md);
    text-decoration: none;
    transition: all 0.2s ease;
    cursor: pointer;
    border: none;
}

.btn-primary {
    background: var(--color-accent);
    color: var(--color-white);
}

.btn-primary:hover {
    background: var(--color-accent-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--color-white);
    color: var(--color-primary);
    border: 1px solid var(--color-border);
}

.btn-secondary:hover {
    border-color: var(--color-accent);
    color: var(--color-accent);
}

/* Hero Stats */
.hero-stats {
    display: grid;
    gap: var(--spacing-md);
}

.stat-card {
    background: var(--color-white);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--color-border);
}

.stat-number {
    font-size: 3rem;
    font-weight: 700;
    color: var(--color-accent);
    line-height: 1;
    margin-bottom: var(--spacing-xs);
}

.stat-label {
    font-size: 0.9375rem;
    color: var(--color-secondary);
}

/* ============================================
   Section Styles
   ============================================ */
.directions,
.timeline-section,
.about-site {
    padding: var(--spacing-2xl) 0;
}

.section-title {
    font-size: 2rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--spacing-xs);
    color: var(--color-primary);
}

.section-subtitle {
    font-size: 1.125rem;
    color: var(--color-secondary);
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

/* ============================================
   Directions Grid
   ============================================ */
.directions-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-lg);
}

/* 4列布局（用于首页4个方向） */
.directions-grid.four-columns {
    grid-template-columns: repeat(2, 1fr);
}

.direction-card {
    background: var(--color-white);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    text-decoration: none;
    color: inherit;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.direction-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--color-border);
    transition: all 0.3s ease;
}

.direction-card:nth-child(1)::before { background: var(--color-ai); }
.direction-card:nth-child(2)::before { background: var(--color-low); }
.direction-card:nth-child(3)::before { background: var(--color-biz); }

.direction-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: transparent;
}

.direction-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-sm);
}

.direction-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--color-primary);
}

.direction-card p {
    font-size: 0.9375rem;
    color: var(--color-secondary);
    margin-bottom: var(--spacing-md);
    line-height: 1.6;
}

.direction-works {
    list-style: none;
    margin-bottom: var(--spacing-md);
}

.direction-works li {
    font-size: 0.875rem;
    color: var(--color-muted);
    padding: 0.25rem 0;
    padding-left: 1.25rem;
    position: relative;
}

.direction-works li::before {
    content: '•';
    position: absolute;
    left: 0;
    color: var(--color-accent);
}

.direction-link {
    font-size: 0.875rem;
    color: var(--color-accent);
    font-weight: 500;
}

/* ============================================
   Timeline
   ============================================ */
.timeline {
    max-width: 800px;
    margin: 0 auto;
    position: relative;
    padding-left: 40px;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 11px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--color-border);
}

.timeline-item {
    position: relative;
    padding-bottom: var(--spacing-xl);
}

.timeline-item:last-child {
    padding-bottom: 0;
}

.timeline-marker {
    position: absolute;
    left: -40px;
    top: 4px;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: var(--color-white);
    border: 3px solid var(--color-accent);
    box-shadow: 0 0 0 4px var(--color-white);
}

.timeline-date {
    font-size: 0.875rem;
    color: var(--color-accent);
    font-weight: 500;
    margin-bottom: var(--spacing-xs);
}

.timeline-content h3 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
    color: var(--color-primary);
}

.timeline-content p {
    font-size: 0.9375rem;
    color: var(--color-secondary);
    line-height: 1.6;
}

/* ============================================
   About Site Section
   ============================================ */
.about-site {
    background: var(--color-light);
}

.about-site-content {
    max-width: 800px;
    margin: 0 auto;
    text-align: center;
}

.about-site-content h2 {
    font-size: 1.75rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--color-primary);
}

.about-site-content p {
    font-size: 1rem;
    color: var(--color-secondary);
    line-height: 1.8;
    margin-bottom: var(--spacing-md);
}

.about-site-content ul {
    list-style: none;
    text-align: left;
    max-width: 500px;
    margin: 0 auto var(--spacing-md);
}

.about-site-content li {
    padding: var(--spacing-xs) 0;
    padding-left: 1.75rem;
    position: relative;
    color: var(--color-secondary);
}

.about-site-content li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--color-accent);
    font-weight: 600;
}

/* ============================================
   Footer
   ============================================ */
.footer {
    background: var(--color-primary);
    color: var(--color-white);
    padding: var(--spacing-xl) 0 var(--spacing-md);
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
}

.footer-brand h4 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.footer-brand p {
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.7);
}

.footer-nav {
    display: flex;
    gap: var(--spacing-lg);
}

.footer-nav a {
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.7);
    text-decoration: none;
    transition: color 0.2s ease;
}

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

.footer-bottom {
    text-align: center;
    padding-top: var(--spacing-md);
    border-top: 1px solid rgba(255, 255, 255, 0.1);
}

.footer-bottom p {
    font-size: 0.8125rem;
    color: rgba(255, 255, 255, 0.5);
}

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 768px) {
    .nav-menu {
        position: fixed;
        top: 70px;
        left: 0;
        right: 0;
        background: var(--color-white);
        flex-direction: column;
        padding: var(--spacing-md);
        gap: 0;
        border-bottom: 1px solid var(--color-border);
        transform: translateY(-100%);
        opacity: 0;
        transition: all 0.3s ease;
        pointer-events: none;
    }

    .nav-menu.active {
        transform: translateY(0);
        opacity: 1;
        pointer-events: all;
    }

    .nav-menu li {
        padding: var(--spacing-sm) 0;
    }

    .nav-toggle {
        display: flex;
    }

    .hero-content {
        grid-template-columns: 1fr;
        gap: var(--spacing-lg);
    }

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

    .hero-stats {
        grid-template-columns: repeat(3, 1fr);
        gap: var(--spacing-sm);
    }

    .stat-card {
        padding: var(--spacing-md);
    }

    .stat-number {
        font-size: 2rem;
    }

    .directions-grid {
        grid-template-columns: 1fr !important;
    }

    .section-title {
        font-size: 1.5rem;
    }

    .timeline {
        padding-left: 30px;
    }

    .timeline-marker {
        left: -30px;
        width: 20px;
        height: 20px;
    }

    .footer-content {
        flex-direction: column;
        gap: var(--spacing-md);
        text-align: center;
    }

    .footer-nav {
        flex-direction: column;
        gap: var(--spacing-sm);
    }
}

@media (max-width: 480px) {
    .hero-actions {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }

    .hero-stats {
        grid-template-columns: 1fr;
    }
}