/* --- 1. 核心变量与基础重置 --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&display=swap');

:root {
    --primary: #000000;
    --accent: #0071e3;       /* 苹果蓝 */
    --brand-dark: #003366;   
    --text-sub: #86868b;    
    --bg-light: #fbfbfb;
    --glass: rgba(255, 255, 255, 0.75);
    --transition: all 0.5s cubic-bezier(0.28, 0.11, 0.32, 1);
}

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

html {
    /* 核心修复：防止滚动条出现时页面水平抖动 */
    scrollbar-gutter: stable;
}

body {
    font-family: 'Inter', -apple-system, sans-serif;
    color: var(--primary);
    background: #ffffff;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
}

/* --- 2. 导航栏 (彻底解决跳动) --- */
nav {
    position: fixed;
    top: 20px;            /* 统一所有页面的间距 */
    left: 50%;
    transform: translateX(-50%);
    width: 90%; 
    max-width: 1100px;    
    display: flex; 
    justify-content: space-between; 
    align-items: center;
    padding: 12px 24px;   /* 统一内边距 */
    background: var(--glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    z-index: 1000;
    border-radius: 40px;
    border: 1px solid rgba(0, 0, 0, 0.05);
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.03);
}

.logo-container img {
    height: 26px;         /* 统一 Logo 高度 */
    width: auto;
    display: block;
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 32px;            
}

.nav-links a {
    text-decoration: none;
    color: var(--primary);
    font-size: 0.85rem;   
    font-weight: 500;
    opacity: 0.7;
    transition: var(--transition);
}

.nav-links a:hover {
    opacity: 1;
    color: var(--accent);
}

#lang-btn {
    background: var(--primary);
    color: white;
    border: none;
    padding: 7px 18px;    
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

/* --- 3. 通用 Hero 与布局 --- */
.hero {
    position: relative;
    height: 45vh;         /* 针对 About/Contact 优化的高度 */
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    background: #fff;
    padding-top: 80px;
}

.hero-content h1 {
    font-size: clamp(2.2rem, 5vw, 3.5rem);
    font-weight: 700;
    letter-spacing: -0.04em;
}

.section {
    padding: 60px 10% 100px;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
}

/* 通用卡片样式 */
.card {
    background: var(--bg-light);
    padding: 35px;
    border-radius: 20px;
    border: 1px solid #f2f2f2;
    transition: var(--transition);
}

.card:hover {
    background: #ffffff;
    box-shadow: 0 15px 35px rgba(0,0,0,0.05);
    transform: translateY(-5px);
}

/* --- 4. 移动端底部导航 --- */
.mobile-bottom-nav {
    display: none; /* 默认隐藏 */
}

@media (max-width: 768px) {
    nav {
        width: 95%;
        top: 15px;
    }
    
    .nav-links {
        display: none; /* 手机端隐藏顶部链接 */
    }

    .mobile-bottom-nav {
        display: flex;
        position: fixed;
        bottom: 20px;
        left: 50%;
        transform: translateX(-50%);
        width: 92%;
        max-width: 400px;
        background: rgba(0, 0, 0, 0.85);
        backdrop-filter: blur(15px);
        -webkit-backdrop-filter: blur(15px);
        padding: 12px 10px;
        border-radius: 30px;
        justify-content: space-around;
        z-index: 2000;
    }

    .mobile-bottom-nav a {
        color: #fff;
        text-decoration: none;
        font-size: 0.65rem;
        display: flex;
        flex-direction: column;
        align-items: center;
        gap: 4px;
        opacity: 0.6;
    }

    .mobile-bottom-nav a.active {
        color: var(--accent);
        opacity: 1;
    }
}

/* --- 5. 页脚 --- */
footer {
    padding: 60px 10% 120px; 
    text-align: center;
    color: var(--text-sub);
    font-size: 0.8rem;
    border-top: 1px solid #f2f2f2;
}