/* =========================================
   1. 全局变量与重置 (Variables & Resets)
   ========================================= */
:root {
    --primary: #0038A8;     /* 沉稳海运蓝 */
    --secondary: #009B3A;   /* 巴西绿 */
    --accent: #FEDF00;      /* 巴西黄 */
    --dark: #2C3E50;        /* 深灰字体 */
    --light: #F8F9FA;       /* 浅色背景 */
    --white: #FFFFFF;
    --border: #EAEAEA;
    --shadow: 0 4px 12px rgba(0,0,0,0.08);
    --transition: all 0.3s ease;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'PingFang SC', 'Helvetica Neue', Helvetica, Arial, sans-serif;
    color: var(--dark);
    background-color: var(--white);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* =========================================
   2. 布局系统 (Layout & Grid)
   ========================================= */
.container {
    width: 90%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 15px;
}

.grid {
    display: grid;
    gap: 30px;
}

/* 响应式网格：手机1列，平板2列，PC多列 */
.grid-2 { grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); }
.grid-3 { grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); }
.grid-4 { grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); }

.section-padding {
    padding: 80px 0;
}

.text-center {
    text-align: center;
}

/* =========================================
   3. 通用组件 (UI Components)
   ========================================= */
.btn {
    display: inline-block;
    padding: 12px 28px;
    background-color: var(--primary);
    color: var(--white);
    text-decoration: none;
    border-radius: 6px;
    font-weight: 600;
    border: none;
    cursor: pointer;
    transition: var(--transition);
}

.btn:hover {
    background-color: #002D88;
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.btn-secondary {
    background-color: var(--secondary);
}

.btn-secondary:hover {
    background-color: #007A2E;
}

.section-title {
    font-size: 2.2rem;
    color: var(--dark);
    margin-bottom: 20px;
}

.section-subtitle {
    font-size: 1.1rem;
    color: #666;
    margin-bottom: 50px;
}

/* =========================================
   4. 页眉导航 (Header & Navbar)
   ========================================= */
header {
    background-color: var(--white);
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 80px;
}

.logo {
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--primary);
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 30px;
    list-style: none;
}

.nav-links a {
    text-decoration: none;
    color: var(--dark);
    font-weight: 500;
    transition: var(--transition);
}

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

.menu-toggle {
    display: none;
    font-size: 1.5rem;
    cursor: pointer;
    background: none;
    border: none;
    color: var(--dark);
}

/* =========================================
   5. 页脚 (Footer)
   ========================================= */
footer {
    background-color: var(--dark);
    color: var(--white);
    padding: 60px 0 20px;
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 40px;
    margin-bottom: 40px;
}

.footer-col h4 {
    color: var(--accent);
    margin-bottom: 20px;
    font-size: 1.2rem;
}

.footer-col p, .footer-col a {
    color: #CCC;
    text-decoration: none;
    margin-bottom: 10px;
    display: block;
    transition: var(--transition);
}

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

.footer-bottom {
    text-align: center;
    padding-top: 20px;
    border-top: 1px solid #444;
    color: #888;
    font-size: 0.9rem;
}

/* =========================================
   6. 移动端自适配 (Media Queries)
   ========================================= */
@media (max-width: 768px) {
    .nav-links {
        display: none;
        position: absolute;
        top: 80px;
        left: 0;
        width: 100%;
        background-color: var(--white);
        flex-direction: column;
        align-items: center;
        padding: 20px 0;
        box-shadow: 0 4px 6px rgba(0,0,0,0.05);
    }

    .nav-links.active {
        display: flex;
    }

    .menu-toggle {
        display: block;
    }

    .section-title {
        font-size: 1.8rem;
    }
    
    .section-padding {
        padding: 50px 0;
    }
}