/* 中俄数学交叉研究与应用官网 - 主样式 */
:root {
  --color-bg: #fafbfc;
  --color-surface: #fff;
  --color-primary: #1a365d;
  --color-primary-light: #2c5282;
  --color-accent: #c53030;
  --color-accent-soft: #e53e3e;
  --color-text: #1a202c;
  --color-text-muted: #4a5568;
  --color-border: #e2e8f0;
  --font-serif-zh: 'Noto Serif SC', 'SimSun', serif;
  --font-sans-zh: 'Noto Sans SC', 'Microsoft YaHei', sans-serif;
  --font-serif-en: 'PT Serif', Georgia, serif;
  --font-sans-en: 'Source Sans 3', Arial, sans-serif;
  --shadow: 0 1px 3px rgba(0,0,0,.08);
  --shadow-md: 0 4px 12px rgba(0,0,0,.1);
  --radius: 8px;
  --header-h: 64px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans-zh);
  font-size: 16px;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
}

[lang="ru"] body,
[data-lang="ru"] body { font-family: var(--font-sans-en); }
[lang="en"] body,
[data-lang="en"] body { font-family: var(--font-sans-en); }

.container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Header */
.header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  gap: 24px;
}

.logo {
  font-family: var(--font-serif-zh);
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--color-primary);
  text-decoration: none;
  white-space: nowrap;
}

[data-lang="ru"] .logo,
[data-lang="en"] .logo { font-family: var(--font-serif-en); }

.nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  align-items: center;
}

.nav a {
  color: var(--color-text);
  text-decoration: none;
  font-size: 0.95rem;
  padding: 6px 10px;
  border-radius: var(--radius);
  transition: background .2s, color .2s;
}

.nav a:hover {
  background: var(--color-bg);
  color: var(--color-primary);
}

.lang-switcher {
  display: flex;
  gap: 4px;
}

.lang-btn {
  padding: 6px 12px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-muted);
  font-size: 0.9rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all .2s;
}

.lang-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.lang-btn.active {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: #fff;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 8px;
  background: none;
  border: none;
  cursor: pointer;
}

.nav-toggle span {
  width: 24px;
  height: 2px;
  background: var(--color-text);
}

@media (max-width: 900px) {
  .nav { display: none; }
  .nav.open { display: flex; flex-direction: column; position: absolute; top: var(--header-h); left: 0; right: 0; background: var(--color-surface); padding: 16px; border-bottom: 1px solid var(--color-border); }
  .nav-toggle { display: flex; }
}

/* Hero */
.hero {
  position: relative;
  min-height: 420px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  overflow: hidden;
}

.hero-bg {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-light) 50%, #2d3748 100%);
  opacity: 0.96;
}

.hero-bg::after {
  content: '';
  position: absolute;
  inset: 0;
  background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.04'%3E%3Cpath d='M36 34v-4h-2v4h-4v2h4v4h2v-4h4v-2h-4zm0-30V0h-2v4h-4v2h4v4h2V6h4V4h-4zM6 34v-4H4v4H0v2h4v4h2v-4h4v-2H6zM6 4V0H4v4H0v2h4v4h2V6h4V4H6z'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
  opacity: 0.5;
}

.hero-content {
  position: relative;
  z-index: 1;
  color: #fff;
}

.hero h1 {
  margin: 0 0 12px;
  font-family: var(--font-serif-zh);
  font-weight: 700;
  font-size: clamp(1.5rem, 4vw, 2.2rem);
  line-height: 1.3;
}

[data-lang="ru"] .hero h1,
[data-lang="en"] .hero h1 { font-family: var(--font-serif-en); }

.hero-subtitle {
  margin: 0 0 24px;
  font-size: 1.1rem;
  opacity: 0.95;
}

.btn {
  display: inline-block;
  padding: 12px 28px;
  border-radius: var(--radius);
  font-size: 1rem;
  font-weight: 600;
  text-decoration: none;
  transition: transform .2s, box-shadow .2s;
}

.btn-primary {
  background: #fff;
  color: var(--color-primary);
  border: 2px solid #fff;
}

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

/* Sections */
.section {
  padding: 64px 0;
}

.section-alt {
  background: var(--color-surface);
  box-shadow: 0 -1px 0 var(--color-border);
}

.section-title {
  margin: 0 0 8px;
  font-family: var(--font-serif-zh);
  font-weight: 700;
  font-size: 1.75rem;
  color: var(--color-primary);
}

[data-lang="ru"] .section-title,
[data-lang="en"] .section-title { font-family: var(--font-serif-en); }

.section-subtitle {
  margin: 0 0 32px;
  font-size: 1.05rem;
  color: var(--color-text-muted);
}

.section-desc {
  margin: 0 0 32px;
  max-width: 720px;
  color: var(--color-text);
}

.intro-text {
  font-size: 1.1rem;
  line-height: 1.75;
  margin: 0 0 40px;
  color: var(--color-text);
}

.news-block h2,
.events-block h3,
.resources-block strong,
.contact-block h3 {
  font-size: 1.15rem;
  color: var(--color-primary);
  margin: 0 0 12px;
}

.news-list {
  margin: 0;
  padding-left: 1.25rem;
}

.news-list li {
  margin-bottom: 8px;
}

/* Cards */
.cards {
  display: grid;
  gap: 24px;
}

.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }

@media (max-width: 700px) {
  .grid-2, .grid-3 { grid-template-columns: 1fr; }
}

.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  transition: box-shadow .2s, border-color .2s;
}

.card:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--color-primary-light);
}

.card-highlight {
  border-left: 4px solid var(--color-primary);
}

.card h3 {
  margin: 0 0 12px;
  font-size: 1.15rem;
  color: var(--color-primary);
}

.card p {
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

/* Jobs */
.jobs-contact {
  margin-top: 24px;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

/* Achievements */
.achievements-list {
  margin: 0;
  padding-left: 1.25rem;
  max-width: 640px;
}

.achievements-list li {
  margin-bottom: 12px;
  line-height: 1.6;
}

/* Events / Resources */
.events-block,
.resources-block {
  margin-top: 24px;
}

.events-block h3,
.resources-block strong { margin-top: 20px; }
.events-block h3:first-child,
.resources-block p:first-child { margin-top: 0; }

.muted { color: var(--color-text-muted); }
.small { font-size: 0.9rem; }

/* About / Contact */
.about-intro {
  margin-bottom: 40px;
}

.contact-block {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 28px;
  max-width: 520px;
  box-shadow: var(--shadow);
}

.contact-item {
  margin: 8px 0;
}

.contact-item a {
  color: var(--color-primary);
  text-decoration: none;
}

.contact-item a:hover {
  text-decoration: underline;
}

.contact-address {
  line-height: 1.6;
}

/* 来华工作邀请申请表单 - 按语言显示 */
.form-lang-en,
.form-lang-ru { display: none; }
.form-lang-zh { display: block; }
[data-lang="en"] .form-lang-zh { display: none; }
[data-lang="en"] .form-lang-en { display: block; }
[data-lang="en"] .form-lang-ru { display: none; }
[data-lang="ru"] .form-lang-zh { display: none; }
[data-lang="ru"] .form-lang-en { display: none; }
[data-lang="ru"] .form-lang-ru { display: block; }

.form-doc {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 28px 32px;
  margin-top: 24px;
  max-width: 800px;
}

.form-doc h3 {
  margin: 24px 0 10px;
  font-size: 1.05rem;
  color: var(--color-primary);
}

.form-doc h3:first-child {
  margin-top: 0;
}

.form-doc p {
  margin: 6px 0;
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--color-text);
}

.form-sign {
  margin-top: 28px;
  padding-top: 20px;
  border-top: 1px dashed var(--color-border);
}

.form-sign .mt {
  margin-top: 16px;
}

/* Footer */
.footer {
  background: var(--color-primary);
  color: rgba(255,255,255,.9);
  padding: 40px 0;
  margin-top: 0;
}

.footer-inner {
  text-align: center;
}

.footer-copy {
  margin: 0 0 8px;
  font-weight: 600;
}

.footer-address {
  margin: 0 0 8px;
  font-size: 0.95rem;
  opacity: 0.9;
}

.footer a {
  color: #fff;
  text-decoration: underline;
}

.footer a:hover {
  opacity: 0.9;
}