/* ==================== 全局和基本样式 ==================== */
:root {
    --primary-color: #3498db;
    --dark-color: #333;
    --light-color: #f4f4f4;
    --text-color: #555;
    --container-width: 80%;
}

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

body {
    font-family: 'Helvetica Neue', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
    line-height: 1.6;
    background: #fff;
    color: var(--text-color);
}

html {
    scroll-behavior: smooth;
}

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

ul {
    list-style: none;
}

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

.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 2rem 0;
}

/* ==================== Header / 头部 ==================== */
#header {
    background: #fff;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
    width: 100%;
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: 1rem;
    padding-bottom: 1rem;
}

.logo {
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--dark-color);
}

/* 桌面端导航 */
.main-nav .nav-links {
    display: flex;
}

.main-nav .nav-links li {
    margin-left: 2rem;
}

.main-nav a {
    color: var(--dark-color);
    font-weight: 500;
    transition: color 0.3s ease;
}

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

/* 汉堡菜单按钮 (默认隐藏) */
.hamburger {
    display: none;
    cursor: pointer;
    background: transparent;
    border: none;
    padding: 0;
}

.bar {
    display: block;
    width: 25px;
    height: 3px;
    margin: 5px auto;
    background-color: var(--dark-color);
    transition: all 0.3s ease-in-out;
}

/* ==================== Slider / 幻灯片 ==================== */
.slider-container {
    position: relative;
    width: 100%;
    height: 900px;
    max-height: 100vh;
    overflow: hidden;
    background-color: var(--dark-color);
}
.slides-wrapper { display: flex; width: 100%; height: 100%; }
.slide { min-width: 100%; height: 100%; opacity: 0; transition: opacity 1s ease-in-out; visibility: hidden; position: absolute; left: 0; top: 0; }
.slide.active { opacity: 1; visibility: visible; }
.slide img { width: 100%; height: 100%; object-fit: cover; }
.slide-content { position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); color: #fff; text-align: center; }
.slide-content h1 { font-size: 3rem; margin-bottom: 0.5rem; text-shadow: 4px 4px 4px rgba(0,0,0,0.7); }
.slide-content p { font-size: 1.5rem; margin-bottom: 1.5rem; text-shadow: 2px 2px 2px rgba(0,0,0,0.7); }
.btn { display: inline-block; padding: 0.8rem 2rem; background: var(--primary-color); color: #fff; border: none; border-radius: 5px; cursor: pointer; font-size: 1rem; transition: background 0.3s ease; }
.btn:hover { background: #2980b9; }
.slider-arrow { position: absolute; top: 50%; transform: translateY(-50%); background: rgba(0, 0, 0, 0.5); color: #fff; border: none; padding: 1rem; font-size: 1.5rem; cursor: pointer; z-index: 10; transition: background 0.3s ease; }
.slider-arrow:hover { background: rgba(0, 0, 0, 0.8); }
.prev { left: 20px; }
.next { right: 20px; }

/* ==================== Banners / 横幅广告 ==================== */
.banner-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px; }
.banner-item { aspect-ratio: 4 / 3; perspective: 1000px; }
.banner-inner { position: relative; width: 100%; height: 100%; transition: transform 0.8s; transform-style: preserve-3d; }
.banner-item:hover .banner-inner { transform: rotateY(180deg); }
.banner-front, .banner-back { position: absolute; width: 100%; height: 100%; -webkit-backface-visibility: hidden; backface-visibility: hidden; overflow: hidden; border-radius: 10px; }
.banner-front { background: var(--dark-color); color: white; }
.banner-back { transform: rotateY(180deg); }
.banner-front img, .banner-back img { width: 100%; height: 100%; object-fit: cover; }
.banner-front h3 { position: absolute; top: 50%; left: 50%; text-align: center; transform: translate(-50%, -50%); font-size: 1.5rem; text-shadow: 4px 4px 4px rgba(0,0,0,0.7); }

/* ==================== Introduction / 介绍内容 ==================== */
.intro-section { text-align: center; }
.intro-section img { margin: 0 auto 2rem; border-radius: 10px; box-shadow: 0 4px 10px rgba(0,0,0,0.1); }
.intro-section p { width: 90%; margin: 0 auto; text-align: justify; }

/* ==================== Footer / 页脚 ==================== */
#footer { background: var(--dark-color); color: var(--light-color); padding: 2rem 0; }
.footer-container { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 1rem; }
.footer-links a { color: var(--light-color); margin-right: 1rem; transition: color 0.3s ease; }
.footer-links a:hover { color: var(--primary-color); }
.footer-copyright { margin-top: 1rem; width: 100%; text-align: center; font-size: 0.9rem; }

/* ==================== 响应式布局 ==================== */
@media (max-width: 1024px) {
    .banner-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    :root {
        --container-width: 90%;
    }

    /* 移动端导航样式 */
    .main-nav .nav-links {
        display: none; /* 关键：在移动端默认隐藏导航链接 */
        flex-direction: column;
        position: absolute;
        top: 100%; /* 定位在header的下方 */
        left: 0;
        width: 100%;
        background-color: #fff;
        box-shadow: 0 4px 6px rgba(0,0,0,0.1);
        padding-bottom: 1rem;
    }

    .main-nav .nav-links li {
        margin: 0;
        width: 100%;
        text-align: center;
    }

    .main-nav .nav-links a {
        padding: 1rem;
        display: block;
        width: 100%;
        border-bottom: 1px solid var(--light-color);
    }

    .main-nav.is-open .nav-links {
        display: flex; /* 关键：当nav有is-open类时，显示菜单 */
    }

    .hamburger {
        display: block; /* 关键：在移动端显示汉堡按钮 */
        order: 1; /* 确保汉堡按钮在右侧 */
    }

    .hamburger.is-open .bar:nth-child(2) { opacity: 0; }
    .hamburger.is-open .bar:nth-child(1) { transform: translateY(8px) rotate(45deg); }
    .hamburger.is-open .bar:nth-child(3) { transform: translateY(-8px) rotate(-45deg); }

    /* 其他移动端样式 */
    .slider-container { height: 500px; }
    .slide-content h1 { font-size: 2rem; }
    .slide-content p { font-size: 1rem; }
    .banner-grid { grid-template-columns: 1fr; }
    .footer-container { flex-direction: column; text-align: center; }
    .footer-links, .footer-contact { margin-bottom: 1rem; }
}