/* ==========================================================================
   全局变量与基础设置
   ========================================================================== */
:root {
    --primary: #1e3a8a; /* 深蓝色 */
    --secondary: #3b82f6; /* 亮蓝色 */
    --accent: #10b981; /* 强调色：翠绿 */
    --bg-light: #f8fafc;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --card-bg: #ffffff;
}

* { margin: 0; padding: 0; box-sizing: border-box; font-family: 'PingFang SC', 'Microsoft YaHei', sans-serif; }
body { background-color: var(--bg-light); color: var(--text-main); line-height: 1.6; padding-top: 70px; /* 为固定导航栏留出空间 */ }
a { text-decoration: none; color: inherit; transition: color 0.3s ease; }

/* ==========================================================================
   导航栏 (顶部固定，支持响应式)
   ========================================================================== */
.navbar {
    position: fixed; top: 0; left: 0; width: 100%; height: 70px;
    background-color: var(--card-bg); box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    display: flex; justify-content: space-between; align-items: center;
    padding: 0 5%; z-index: 1000;
}
.nav-brand { font-size: 1.5rem; font-weight: bold; color: var(--primary); }
.nav-links { display: flex; gap: 2rem; list-style: none; }
.nav-links a { font-weight: 500; color: var(--text-muted); }
.nav-links a:hover, .nav-links a.active { color: var(--secondary); }

/* ==========================================================================
   通用布局类
   ========================================================================== */
.container { max-width: 1000px; margin: 0 auto; padding: 2rem; min-height: calc(100vh - 150px); }
.page-title { font-size: 2.5rem; color: var(--primary); margin-bottom: 2rem; border-bottom: 3px solid var(--secondary); padding-bottom: 10px; display: inline-block; }
.btn { display: inline-block; padding: 0.8rem 1.5rem; background-color: var(--secondary); color: white; border-radius: 8px; font-weight: bold; transition: background 0.3s, transform 0.2s; }
.btn:hover { background-color: var(--primary); transform: translateY(-2px); color: white; }

/* 卡片样式 */
.card { background: var(--card-bg); border-radius: 12px; padding: 2rem; box-shadow: 0 4px 6px rgba(0,0,0,0.02); margin-bottom: 1.5rem; border: 1px solid #e2e8f0; transition: transform 0.3s; }
.card:hover { transform: translateY(-5px); box-shadow: 0 10px 15px rgba(0,0,0,0.05); }

/* ==========================================================================
   移动端响应式适配 (核心)
   ========================================================================== */
@media (max-width: 768px) {
    .navbar { padding: 0 1rem; }
    .nav-links { gap: 1rem; font-size: 0.9rem; } /* 移动端导航栏紧凑一些 */
    .container { padding: 1.5rem 1rem; }
    .page-title { font-size: 2rem; }
    /* 首页特定适配 */
    .hero-section { flex-direction: column; text-align: center; }
    .hero-text { margin-top: 1.5rem; }
    .skills-grid { grid-template-columns: 1fr !important; }
}