/* Layout Essentials / 基础布局 */
:root {
    --bg-white: #ffffff;
    --text-dark: #0f172a;
    --accent-blue: #2563eb;
    --border-gray: #e2e8f0;
}

body {
    font-family: system-ui, -apple-system, sans-serif;
    margin: 0;
    background-color: #f1f5f9;
    color: var(--text-dark);
}

/* NAVIGATION ENGINE / 导航引擎 */
.site-header {
    background: var(--bg-white);
    border-bottom: 2px solid var(--border-gray);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-root {
    display: flex;
    list-style: none;
    margin: 0;
    padding: 0 2rem;
}

.nav-root > li {
    position: relative; /* Anchor for Tier 2 / 二级菜单的锚点 */
}

.nav-root a {
    display: block;
    padding: 1.5rem 1rem;
    text-decoration: none;
    color: inherit;
    font-weight: 500;
}

.nav-root a:hover {
    color: var(--accent-blue);
}

/* DROPDOWN LEVELS / 下拉层级 */

/* Tier 2 & Tier 3 Base / 二级和三级菜单基础样式 */
.sub-menu {
    position: absolute;
    top: 100%;
    left: 0;
    background: white;
    min-width: 200px;
    list-style: none;
    padding: 0.5rem 0;
    margin: 0;
    border: 1px solid var(--border-gray);
    box-shadow: 0 4px 6px -1px rgba(0,0,0,0.1);
    
    /* Animation & Visibility / 动画与可见性 */
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all 0.2s ease;
}

/* Tier 3 Placement (Folding out to the side) / 三级菜单位置（向侧面展开） */
.sub-menu.nested {
    top: 0;
    left: 100%; /* Position it to the right of Level 2 / 置于二级菜单右侧 */
    transform: translateX(10px);
}

/* THE TRIGGER LOGIC / 触发逻辑 */
li:hover > .sub-menu,
li:focus-within > .sub-menu {
    opacity: 1;
    visibility: visible;
    transform: translate(0);
}

/* Styles for dropdown links / 下拉链接样式 */
.sub-menu a {
    padding: 0.75rem 1.25rem;
    font-size: 0.9rem;
    border-bottom: 1px solid #f8fafc;
}

.sub-menu li:last-child a {
    border-bottom: none;
}

/* RENDERED EXPLANATION / 说明板块 */
.explanation-area {
    max-width: 1000px;
    margin: 4rem auto;
    padding: 0 1rem;
}

.info-card {
    background: white;
    padding: 2.5rem;
    border-radius: 12px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

.content-split {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    margin-top: 2rem;
}

@media (max-width: 768px) {
    .content-split { grid-template-columns: 1fr; }
    .nav-root { flex-direction: column; padding: 0; }
    .sub-menu, .sub-menu.nested { 
        position: static; 
        opacity: 1; 
        visibility: visible; 
        transform: none; 
        box-shadow: none; 
        border: none;
        padding-left: 1.5rem;
    }
}
/* SEO Insight Box Styling */
.seo-insight-box {
    max-width: 1000px;
    margin: 2rem auto;
    padding: 2rem;
    background: #ffffff;
    border-radius: 12px;
    border: 1px solid var(--border-gray);
}

.seo-insight-box h2 {
    color: var(--accent-blue);
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    border-bottom: 2px solid var(--f1f5f9);
    padding-bottom: 0.5rem;
}

.insight-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
}

.seo-insight-box p {
    font-size: 0.95rem;
    line-height: 1.6;
    margin-bottom: 1rem;
}

.seo-insight-box p[lang="zh"] {
    color: #64748b;
    font-size: 0.9rem;
}

/* Footer Styling */
.pattern-footer {
    max-width: 1000px;
    margin: 4rem auto;
    padding: 2rem 1rem;
    text-align: center;
}

.back-nav a {
    color: var(--accent-blue);
    text-decoration: none;
    font-weight: 600;
}

.corporate-links {
    margin-top: 2rem;
    font-size: 0.9rem;
    color: #64748b;
}

.corporate-links a {
    color: var(--accent-blue);
    text-decoration: none;
}

@media (max-width: 768px) {
    .insight-grid { grid-template-columns: 1fr; }
}