:root {
    --bg-color: #f8fafc;
    --text-primary: #0f172a;
    --text-secondary: #64748b;
    --card-bg: #ffffff;
    --card-border: rgba(255, 255, 255, 0.8);
    --accent-primary: #6366f1;
    --accent-secondary: #ec4899;
    --card-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
    --card-shadow-hover: 0 20px 25px -5px rgba(0, 0, 0, 0.05), 0 10px 10px -5px rgba(0, 0, 0, 0.02);
    --icon-bg: #f8fafc;
    --icon-bg-hover: #eff6ff;
    --shape-color-1: #c7d2fe;
    --shape-color-2: #fbcfe8;
    --shape-opacity: 0.6;
    --toggle-color: #0f172a;
    --toggle-bg: rgba(0, 0, 0, 0.05);
    --toggle-bg-hover: rgba(0, 0, 0, 0.1);
}

[data-theme="dark"] {
    --bg-color: #020617;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --card-bg: rgba(15, 23, 42, 0.85);
    --card-border: rgba(255, 255, 255, 0.15);
    --card-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.5);
    --card-shadow-hover: 0 20px 25px -5px rgba(0, 0, 0, 0.7);
    --icon-bg: rgba(255, 255, 255, 0.1);
    --icon-bg-hover: rgba(255, 255, 255, 0.15);
    --shape-color-1: #1e3a8a;
    --shape-color-2: #5b21b6;
    --shape-opacity: 0.25;
    --toggle-color: #f1f5f9;
    --toggle-bg: rgba(255, 255, 255, 0.1);
    --toggle-bg-hover: rgba(255, 255, 255, 0.2);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    position: relative;
    overflow-x: hidden;
    transition: background-color 0.5s ease, color 0.5s ease;
}

/* 抽象背景图形 */
.bg-shape {
    position: fixed;
    border-radius: 50%;
    filter: blur(80px);
    z-index: -1;
    opacity: var(--shape-opacity);
    animation: float 20s infinite alternate ease-in-out;
    transition: background 0.5s ease, opacity 0.5s ease;
}

.shape-1 {
    width: 600px;
    height: 600px;
    background: var(--shape-color-1);
    top: -100px;
    right: -100px;
}

.shape-2 {
    width: 500px;
    height: 500px;
    background: var(--shape-color-2);
    bottom: -100px;
    left: -100px;
    animation-delay: -5s;
}

/* 主题切换按钮 */
#theme-toggle {
    position: absolute;
    top: 2rem;
    right: 2rem;
    width: 3rem;
    height: 3rem;
    border-radius: 50%;
    border: none;
    background: var(--toggle-bg);
    color: var(--toggle-color);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    z-index: 10;
}

#theme-toggle:hover {
    background: var(--toggle-bg-hover);
    transform: rotate(15deg);
}

.sun-icon {
    display: none;
}

.moon-icon {
    display: block;
}

[data-theme="dark"] .sun-icon {
    display: block;
}

[data-theme="dark"] .moon-icon {
    display: none;
}

.container {
    width: 100%;
    max-width: 1200px;
    padding: 1.5rem;
    z-index: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    min-height: 100vh;
}

header {
    text-align: left;
    margin-bottom: 2rem;
    position: relative;
    flex-shrink: 0;
}

header::after {
    content: '';
    position: absolute;
    bottom: -0.5rem;
    left: 0;
    width: 60px;
    height: 4px;
    background: linear-gradient(90deg, var(--accent-primary), var(--accent-secondary));
    border-radius: 2px;
}

h1 {
    font-size: 3rem;
    font-weight: 900;
    letter-spacing: -0.03em;
    color: var(--text-primary);
    margin-bottom: 0.25rem;
    line-height: 1.1;
    transition: color 0.5s ease;
}

p.subtitle {
    color: var(--text-secondary);
    font-size: 1.1rem;
    font-weight: 500;
    transition: color 0.5s ease;
}

.nav-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    width: 100%;
    flex-grow: 1;
    align-content: center;
}

.nav-card {
    background: var(--card-bg);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    padding: 2rem;
    border-radius: 1.25rem;
    text-decoration: none;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    position: relative;
    box-shadow: var(--card-shadow);
    border: 1px solid var(--card-border);
    overflow: hidden;
}

.nav-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--card-shadow-hover);
}

.card-icon {
    font-size: 2rem;
    margin-bottom: 1rem;
    background: var(--icon-bg);
    width: 56px;
    height: 56px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 1rem;
    transition: transform 0.3s ease, background 0.3s ease;
}

.nav-card:hover .card-icon {
    transform: rotate(-10deg) scale(1.1);
    background: var(--icon-bg-hover);
}

.card-title {
    font-size: 1.35rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: color 0.5s ease;
}

.card-arrow {
    opacity: 0;
    transform: translateX(-10px);
    transition: all 0.3s ease;
    color: var(--accent-primary);
}

.nav-card:hover .card-arrow {
    opacity: 1;
    transform: translateX(0);
}

.card-desc {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.5;
    transition: color 0.5s ease;
}

footer {
    margin-top: 2rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--card-border);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.75rem;
    color: var(--text-secondary);
    font-size: 0.85rem;
    width: 100%;
    transition: border-color 0.5s ease, color 0.5s ease;
    flex-shrink: 0;
}

.author-tag {
    font-weight: 600;
    color: var(--text-primary);
    background: var(--icon-bg);
    padding: 0.25rem 0.75rem;
    border-radius: 999px;
    font-size: 0.75rem;
    transition: background 0.5s ease, color 0.5s ease;
}

footer a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color 0.2s;
}

footer a:hover {
    color: var(--accent-primary);
}

@keyframes float {
    0% { transform: translate(0, 0); }
    100% { transform: translate(30px, 30px); }
}

@media (max-width: 640px) {
    h1 { font-size: 2.5rem; }
    .container { padding: 1.5rem; }
    header { text-align: center; margin-bottom: 3rem; }
    header::after { left: 50%; transform: translateX(-50%); }
    .nav-card { align-items: center; text-align: center; }
    #theme-toggle { top: 1rem; right: 1rem; }
}