/* ===== 全局重置与基础 ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  /* 主色调系统 */
  --color-primary: #4a9e6d;     /* 草绿 - 生长感 */
  --color-secondary: #5a6b7c;  /* 青灰 - 理性与温度 */
  --color-light: #f9fbfa;      /* 暖白背景 */
  --color-dark: #2d3742;       /* 深灰文字 */
  --color-border: #e2e8f0;     /* 浅灰边框 */
  --radius: 8px;
  --shadow: 0 2px 12px rgba(0,0,0,0.05);
  --transition: all 0.3s ease;
}

body {
  font-family: "Source Han Sans SC", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.6;
  color: var(--color-dark);
  background-color: var(--color-light);
  overflow-x: hidden;
}

.container {
  width: 90%;
  max-width: 1024px;
  margin: 0 auto;
}

.section {
  padding: 6rem 0;
}

.section-title {
  text-align: center;
  font-size: 2.2rem;
  font-weight: 700;
  color: var(--color-secondary);
  margin-bottom: 3rem;
  position: relative;
}
.section-title::after {
  content: '';
  display: block;
  width: 60px;
  height: 4px;
  background: var(--color-primary);
  margin: 0.8rem auto;
  border-radius: 2px;
}

/* ===== 头部与导航 ===== */
.header {
  background: white;
  box-shadow: var(--shadow);
  position: sticky;
  top: 0;
  z-index: 100;
}

.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.2rem 0;
}

.logo {
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--color-primary);
  text-decoration: none;
}

.menu-toggle {
  display: none;
  flex-direction: column;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.menu-toggle span {
  width: 24px;
  height: 3px;
  background: var(--color-dark);
  margin: 3px 0;
  transition: var(--transition);
}

.nav-list {
  display: flex;
  list-style: none;
}
.nav-list a {
  text-decoration: none;
  color: var(--color-dark);
  font-weight: 500;
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
  transition: var(--transition);
}
.nav-list a:hover {
  color: var(--color-primary);
  background: rgba(74, 158, 109, 0.08);
}

.hero {
  padding: 6rem 0 4rem;
  text-align: center;
  max-width: 800px;
  margin: 0 auto;
}
.hero h1 {
  font-size: 3.2rem;
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 1.2rem;
  color: var(--color-secondary);
}
.hero .subtitle {
  font-size: 1.3rem;
  color: #64748b;
  margin-bottom: 2.5rem;
  font-weight: 400;
}
.hero-actions {
  display: flex;
  justify-content: center;
  gap: 1.2rem;
  flex-wrap: wrap;
}
.scroll-indicator {
  margin-top: 3rem;
  text-align: center;
}
.scroll-indicator span {
  display: inline-block;
  font-size: 0.9rem;
  color: #94a3b8;
  animation: bounce 2s infinite;
}
@keyframes bounce {
  0%, 20%, 50%, 80%, 100% {transform: translateY(0);}
  40% {transform: translateY(-10px);}
  60% {transform: translateY(-5px);}
}

/* ===== 按钮 ===== */
.btn {
  display: inline-block;
  padding: 0.75rem 1.8rem;
  border-radius: var(--radius);
  font-weight: 600;
  text-decoration: none;
  transition: var(--transition);
  border: none;
  cursor: pointer;
  font-size: 1rem;
}
.btn-primary {
  background: var(--color-primary);
  color: white;
}
.btn-primary:hover {
  background: #3a8a5a;
  transform: translateY(-2px);
}
.btn-outline {
  background: transparent;
  color: var(--color-primary);
  border: 2px solid var(--color-primary);
}
.btn-outline:hover {
  background: rgba(74, 158, 109, 0.08);
}
.btn-sm {
  padding: 0.5rem 1.2rem;
  font-size: 0.9rem;
}

/* ===== 项目卡片 ===== */
.project-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.8rem;
}
.project-card {
  background: white;
  border-radius: var(--radius);
  padding: 1.8rem;
  box-shadow: var(--shadow);
  transition: var(--transition);
}
.project-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 6px 20px rgba(0,0,0,0.06);
}
.project-card h3 {
  font-size: 1.4rem;
  margin-bottom: 0.8rem;
  color: var(--color-secondary);
}
.project-card p {
  color: #4a5568;
  margin-bottom: 1rem;
}
.tag {
  display: inline-block;
  font-size: 0.8rem;
  padding: 0.3rem 0.8rem;
  background: rgba(74, 158, 109, 0.1);
  color: var(--color-primary);
  border-radius: 20px;
}

/* ===== 加入板块 ===== */
.join .lead {
  text-align: center;
  font-size: 1.3rem;
  max-width: 700px;
  margin: 0 auto 2.5rem;
  color: var(--color-secondary);
}

.join-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.8rem;
}
.option-card {
  background: white;
  border-radius: var(--radius);
  padding: 1.8rem;
  box-shadow: var(--shadow);
  text-align: center;
}
.option-card h3 {
  font-size: 1.3rem;
  margin-bottom: 0.8rem;
  color: var(--color-secondary);
}
.option-card p {
  color: #4a5568;
  margin-bottom: 1.2rem;
  font-size: 0.95rem;
}

/* ===== 页脚 ===== */
.footer {
  background: var(--color-dark);
  color: #a0aec0;
  padding: 3rem 0 2rem;
}
.footer-text {
  text-align: center;
  margin-bottom: 1rem;
  line-height: 1.7;
}
.footer-note {
  text-align: center;
  font-size: 0.9rem;
  opacity: 0.8;
}

/* ===== 响应式 ===== */
@media (max-width: 768px) {
  .navbar {
    flex-wrap: wrap;
  }
  .nav-list {
    display: none;
    flex-direction: column;
    width: 100%;
    margin-top: 1rem;
  }
  .nav-list.active {
    display: flex;
  }
  .hero h1 {
    font-size: 2.4rem;
  }
  .hero .subtitle {
    font-size: 1.1rem;
  }
  .hero-actions {
    flex-direction: column;
    align-items: center;
  }
  .section {
    padding: 4rem 0;
  }
  .section-title {
    font-size: 1.8rem;
  }
}

@media (max-width: 480px) {
  .menu-toggle {
    display: flex;
  }
  .logo {
    font-size: 1.3rem;
  }
  .hero {
    padding: 4rem 0 2.5rem;
  }
  .hero h1 {
    font-size: 2rem;
  }
}

/* ===== 动画辅助 ===== */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}