/* ==========================================================================
   主样式表 (Main Styles)
   定义设计令牌、基础排版及组件样式
   ========================================================================== */

:root {
    /* --- 颜色系统 (Color System) --- */
    --color-primary: #2C2C2C;       /* 深炭灰 - 主标题/深色背景 */
    --color-secondary: #F8F8F8;     /* 浅灰 - 页面背景/浅色区块 */
    --color-white: #FFFFFF;         /* 纯白 - 卡片背景/文字 */
    
    --color-accent-blue: #0A2463;   /* 深海蓝 - 强调色/按钮 */
    --color-accent-sand: #D4B483;   /* 暖沙色 - 强调色/高亮 */
    
    --color-text-main: #333333;     /* 深灰 - 正文主要文字 */
    --color-text-light: #666666;    /* 中灰 - 辅助文字/副标题 */
    --color-border: #E5E5E5;        /* 边框颜色 */
    --color-border-light: #F0F0F0;  /* 浅边框 */
    --color-bg-light: #F9F9F9;      /* 浅色背景 */

    /* --- 字体系统 (Typography) --- */
    --font-family-en: 'Inter', 'Helvetica Neue', Helvetica, Arial, sans-serif;
    --font-family-cn: 'Noto Sans SC', 'Source Han Sans CN', 'Microsoft YaHei', sans-serif;
    
    /* 字号 */
    --font-size-h1: 3rem;           /* 48px */
    --font-size-h2: 2.25rem;        /* 36px */
    --font-size-h3: 1.5rem;         /* 24px */
    --font-size-h4: 1.25rem;        /* 20px */
    --font-size-body: 1rem;         /* 16px */
    --font-size-small: 0.875rem;    /* 14px */

    /* --- 间距系统 (Spacing) --- */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 2rem;
    --spacing-lg: 4rem;
    --spacing-xl: 6rem;

    /* --- 其它 (Misc) --- */
    --border-radius: 2px; /* 极简风格倾向于直角或微圆角 */
    --transition-base: 0.3s ease;
    --transition-slow: 0.5s ease;
    --shadow-sm: 0 2px 4px rgba(0,0,0,0.03);
    --shadow-md: 0 8px 16px rgba(0,0,0,0.06);
    --shadow-lg: 0 15px 30px rgba(0,0,0,0.08);
}

/* ==========================================================================
   重置与基础 (Reset & Base)
   ========================================================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: var(--font-family-cn);
    font-weight: 400;
    line-height: 1.7;
    color: var(--color-text-main);
    background-color: var(--color-white);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    overflow-x: hidden;
}

/* ==========================================================================
   排版 (Typography)
   ========================================================================== */
h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-family-cn);
    font-weight: 500;
    line-height: 1.3;
    color: var(--color-primary);
    margin-bottom: 1rem;
}

h1 { font-size: var(--font-size-h1); letter-spacing: -0.02em; }
h2 { font-size: var(--font-size-h2); letter-spacing: -0.01em; margin-bottom: 1.5rem; }
h3 { font-size: var(--font-size-h3); margin-bottom: 1rem; }
h4 { font-size: var(--font-size-h4); }

p {
    margin-bottom: 1.5rem;
    font-size: var(--font-size-body);
    color: var(--color-text-light);
}

a {
    color: inherit;
    text-decoration: none;
    transition: color var(--transition-base);
}

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

ul, ol {
    list-style: none;
}

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

/* ==========================================================================
   组件样式 (Components)
   ========================================================================== */

/* --- 按钮 (Buttons) --- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 12px 32px;
    font-size: 0.9rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    cursor: pointer;
    transition: all var(--transition-base);
    border: 1px solid transparent;
    text-align: center;
    white-space: nowrap;
}

.btn-primary {
    background-color: transparent;
    border-color: var(--color-white);
    color: var(--color-white);
}

.btn-primary:hover {
    background-color: var(--color-white);
    color: var(--color-primary);
}

.btn-secondary {
    background-color: transparent;
    border-color: var(--color-primary);
    color: var(--color-primary);
}

.btn-secondary:hover {
    background-color: var(--color-primary);
    color: var(--color-white);
}

.btn-outline {
    background-color: transparent;
    border-color: var(--color-border);
    color: var(--color-text-main);
}

.btn-outline:hover {
    border-color: var(--color-primary);
    background-color: var(--color-bg-light);
}

.btn-text {
    padding: 0;
    border: none;
    border-bottom: 1px solid currentColor;
    border-radius: 0;
}

.btn-text:hover {
    color: var(--color-accent-sand);
    border-color: var(--color-accent-sand);
}

/* --- 卡片 (Cards) --- */
.card {
    background-color: var(--color-white);
    transition: transform var(--transition-base), box-shadow var(--transition-base);
    position: relative;
    height: 100%;
}

.card-hover:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.card-content {
    padding: 1.5rem 0;
}

/* --- 分隔线 (Dividers) --- */
.divider {
    width: 100%;
    height: 1px;
    background-color: var(--color-border);
    margin: 3rem 0;
}

.divider-short {
    width: 60px;
    height: 2px;
    background-color: var(--color-accent-sand);
    margin: 1.5rem auto;
}

/* --- 导航链接 (Nav Links) --- */
.nav-link {
    font-size: 0.9rem;
    font-weight: 400;
    color: var(--color-text-main);
    padding: 0.5rem 0;
    position: relative;
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 0;
    height: 1px;
    background-color: var(--color-primary);
    transition: width var(--transition-base);
}

.nav-link:hover::after,
.nav-link.active::after {
    width: 100%;
}

.nav-link.active {
    font-weight: 500;
    color: var(--color-primary);
}

/* --- 文本样式辅助 (Text Utilities) --- */
.text-lead {
    font-size: 1.125rem;
    line-height: 1.8;
    color: var(--color-text-light);
    font-weight: 300;
}

.text-sub {
    font-size: 1rem;
    color: var(--color-text-light);
    margin-bottom: 0.5rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.text-muted { color: var(--color-text-light); }
.text-white { color: var(--color-white); }
.text-primary { color: var(--color-primary); }
.text-accent { color: var(--color-accent-sand); }
.text-uppercase { text-transform: uppercase; }

/* --- 遮罩与覆盖层 --- */
.overlay-dark {
    background: rgba(0, 0, 0, 0.4);
}

.overlay-gradient {
    background: linear-gradient(to top, rgba(0,0,0,0.7) 0%, rgba(0,0,0,0) 100%);
}

/* --- 动画类 (Animations) --- */
.fade-in-up {
    animation: fadeInUp 0.8s ease forwards;
    opacity: 0;
}

@keyframes fadeInUp {
    from { opacity: 0; transform: translateY(30px); }
    to { opacity: 1; transform: translateY(0); }
}

/* 延迟类 */
.delay-100 { animation-delay: 0.1s; }
.delay-200 { animation-delay: 0.2s; }
.delay-300 { animation-delay: 0.3s; }