/* ====== 基础变量 ====== */
:root {
    --bg: hsl(210, 20%, 98%);
    --text: hsl(210, 10%, 29%);
    --text-muted: hsl(210, 10%, 46%);
    --white: #ffffff;
    --navy: hsl(210, 29%, 24%);
    --navy-dark: hsl(210, 29%, 20%);
    --accent: hsl(22, 91%, 54%);
    --accent-hover: hsl(22, 91%, 48%);
    --border: hsl(210, 20%, 90%);
    --shadow-card: 0 8px 25px -8px hsl(210 29% 24% / 0.12);
    --shadow-subtle: 0 2px 8px -2px hsl(210 29% 24% / 0.06);
    --radius: 0.75rem;
    --font-heading: "Playfair Display", serif;
    --font-body: "Montserrat", sans-serif;
}

/* ====== 重置 ====== */
*,
*::before,
*::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    color: var(--text);
    background-color: var(--bg);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
}

a {
    color: inherit;
    text-decoration: none;
}

/* ====== 导航栏 ====== */
.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px 32px;
    background: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid transparent;
    transition: border-color 0.3s ease;
}

.nav.scrolled {
    border-bottom-color: var(--border);
}

.nav-brand {
    font-family: var(--font-heading);
    font-size: 20px;
    font-weight: 600;
    color: var(--navy);
    letter-spacing: -0.3px;
}

.nav-links {
    display: flex;
    gap: 28px;
}

.nav-links a {
    font-size: 14px;
    font-weight: 500;
    color: var(--text-muted);
    transition: color 0.2s ease;
}

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

/* ====== Hero 主视觉 ====== */
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    background: linear-gradient(135deg, var(--navy), var(--navy-dark));
    color: #fff;
    padding: 120px 24px 80px;
}

.hero-content {
    max-width: 640px;
}

.hero-avatar {
    width: 260px;
    height: 260px;
    border-radius: 50%;
    object-fit: cover;
    object-position: center 15%;
    border: 4px solid rgba(255, 255, 255, 0.3);
    margin-bottom: 36px;
    box-shadow: 0 12px 40px -12px rgba(0, 0, 0, 0.4);
}

.hero-greeting {
    font-size: 15px;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 3px;
    color: var(--accent);
    margin-bottom: 20px;
}

.hero-name {
    font-family: var(--font-heading);
    font-size: 64px;
    font-weight: 700;
    line-height: 1.1;
    margin-bottom: 8px;
    letter-spacing: -1px;
}

.hero-subtitle {
    font-family: var(--font-heading);
    font-size: 22px;
    font-weight: 400;
    color: hsl(210, 20%, 80%);
    margin-bottom: 28px;
}

.hero-tagline {
    font-size: 16px;
    line-height: 1.7;
    color: hsl(210, 20%, 72%);
    margin-bottom: 12px;
}

.hero-location {
    font-size: 14px;
    font-weight: 500;
    color: hsl(210, 20%, 62%);
    letter-spacing: 3px;
    text-transform: uppercase;
    margin-bottom: 40px;
}

.hero-actions {
    display: flex;
    gap: 16px;
    justify-content: center;
    flex-wrap: wrap;
}

/* ====== 按钮 ====== */
.btn {
    display: inline-block;
    padding: 12px 28px;
    border-radius: 9999px;
    font-size: 14px;
    font-weight: 600;
    letter-spacing: 0.3px;
    transition: all 0.25s ease;
    cursor: pointer;
}

.btn-primary {
    background: var(--accent);
    color: #fff;
}

.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
    box-shadow: 0 8px 25px -8px hsl(22 91% 54% / 0.4);
}

.btn-outline {
    background: transparent;
    color: #fff;
    border: 2px solid hsl(210, 20%, 70%);
}

.btn-outline:hover {
    border-color: #fff;
    background: rgba(255, 255, 255, 0.08);
}

/* ====== 通用区块 ====== */
.section {
    padding: 100px 24px;
}

.section-alt {
    background: var(--white);
}

.container {
    max-width: 880px;
    margin: 0 auto;
}

.section-title {
    font-family: var(--font-heading);
    font-size: 36px;
    font-weight: 600;
    color: var(--navy);
    text-align: center;
    margin-bottom: 16px;
    letter-spacing: -0.5px;
}

.section-desc {
    text-align: center;
    color: var(--text-muted);
    margin-bottom: 48px;
    font-size: 16px;
}

/* ====== 卡片 ====== */
.about-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
}

@media (max-width: 640px) {
    .about-grid {
        grid-template-columns: 1fr;
    }

    .hero-avatar {
        width: 180px;
        height: 180px;
    }

    .hero-name {
        font-size: 40px;
    }

    .nav {
        padding: 14px 20px;
    }
}

.card {
    background: var(--white);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 32px;
    box-shadow: var(--shadow-subtle);
    transition: box-shadow 0.3s ease, transform 0.3s ease;
}

.card:hover {
    box-shadow: var(--shadow-card);
    transform: translateY(-2px);
}

.card h4 {
    font-family: var(--font-heading);
    font-size: 20px;
    font-weight: 600;
    color: var(--navy);
    margin-bottom: 12px;
}

.card p {
    color: var(--text-muted);
    font-size: 15px;
    line-height: 1.7;
}

.card strong {
    color: var(--navy);
}

/* ====== 研究方向 ====== */
.research-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}

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

.research-card {
    background: var(--white);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 32px 24px;
    text-align: center;
    box-shadow: var(--shadow-subtle);
    transition: box-shadow 0.3s ease, transform 0.3s ease;
}

.research-card:hover {
    box-shadow: var(--shadow-card);
    transform: translateY(-3px);
}

.research-icon {
    font-size: 36px;
    display: block;
    margin-bottom: 14px;
}

.research-card h4 {
    font-family: var(--font-heading);
    font-size: 18px;
    font-weight: 600;
    color: var(--navy);
    margin-bottom: 10px;
}

.research-card p {
    color: var(--text-muted);
    font-size: 14px;
    line-height: 1.7;
}

/* ====== 时间线 ====== */
.timeline {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.timeline-item {
    display: grid;
    grid-template-columns: 140px 1fr;
    gap: 24px;
    align-items: start;
}

@media (max-width: 640px) {
    .timeline-item {
        grid-template-columns: 1fr;
        gap: 6px;
    }
}

.timeline-date {
    font-size: 13px;
    font-weight: 600;
    color: var(--accent);
    text-transform: uppercase;
    letter-spacing: 1px;
    padding-top: 4px;
}

.timeline-content {
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    transition: box-shadow 0.3s ease;
}

.timeline-content:hover {
    box-shadow: var(--shadow-card);
}

.timeline-content h4 {
    font-family: var(--font-heading);
    font-size: 20px;
    font-weight: 600;
    color: var(--navy);
    margin-bottom: 4px;
}

.timeline-org {
    font-size: 14px;
    font-weight: 500;
    color: var(--accent);
    margin-bottom: 10px;
}

.timeline-content p {
    color: var(--text-muted);
    font-size: 14px;
    line-height: 1.7;
}

/* ====== 语言 ====== */
.lang-grid {
    display: flex;
    gap: 16px;
    justify-content: center;
    flex-wrap: wrap;
}

.lang-item {
    display: flex;
    align-items: center;
    gap: 12px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 9999px;
    padding: 12px 24px;
    transition: border-color 0.25s ease;
}

.lang-item:hover {
    border-color: var(--accent);
}

.lang-name {
    font-weight: 600;
    font-size: 15px;
    color: var(--navy);
}

.lang-level {
    font-size: 13px;
    color: var(--text-muted);
    font-weight: 500;
}

.lang-level.native,
.lang-level.fluent {
    color: hsl(160, 60%, 40%);
}

/* ====== 联系链接 ====== */
.contact-links {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 16px;
}

@media (max-width: 640px) {
    .contact-links {
        grid-template-columns: 1fr;
    }
}

.contact-link {
    display: flex;
    align-items: flex-start;
    gap: 14px;
    padding: 20px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    font-size: 15px;
    font-weight: 500;
    color: var(--text);
    transition: all 0.25s ease;
}

.contact-link:hover {
    border-color: var(--accent);
    background: hsl(22, 91%, 54%, 0.04);
    color: var(--accent);
}

.contact-link strong {
    display: block;
    color: var(--navy);
    margin-bottom: 2px;
    font-size: 14px;
}

.contact-detail {
    font-size: 13px;
    color: var(--text-muted);
    font-weight: 400;
    word-break: break-all;
}

.contact-icon {
    font-size: 20px;
    flex-shrink: 0;
    margin-top: 2px;
}

/* ====== 页脚 ====== */
.footer {
    padding: 32px 24px;
    text-align: center;
    background: var(--navy);
    color: hsl(210, 20%, 70%);
    font-size: 13px;
}