/* ====== 自适应设计：手机优先 ====== */
* { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --primary: #1e6fff;
  --primary-dark: #0b54d3;
  --text: #1f2937;
  --text-soft: #4b5563;
  --bg: #f7f9fc;
  --card: #ffffff;
  --border: #e5e7eb;
  --accent: #0aa37f;
  --shadow: 0 4px 16px rgba(15, 23, 42, 0.06);
}

@media (prefers-color-scheme: dark) {
  :root {
    --text: #e5e7eb;
    --text-soft: #9ca3af;
    --bg: #0f172a;
    --card: #1e293b;
    --border: #334155;
    --shadow: 0 4px 16px rgba(0, 0, 0, 0.4);
  }
}

html { -webkit-text-size-adjust: 100%; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial,
    sans-serif;
  font-size: 16px;
  line-height: 1.7;
  color: var(--text);
  background: var(--bg);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
a:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

/* 仅屏幕阅读器可见；同时避免内联样式，便于 CSP 收紧 */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.note { font-size: 0.9rem; }

.container {
  width: 100%;
  max-width: 880px;
  margin: 0 auto;
  padding: 0 20px;
}

/* ====== 顶部导航 ====== */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--card);
  border-bottom: 1px solid var(--border);
  transition: box-shadow 0.2s ease;
}

.site-nav.is-scrolled {
  box-shadow: 0 2px 14px rgba(15, 23, 42, 0.1);
}

.nav-inner {
  display: flex;
  align-items: center;
  gap: 18px;
  height: 48px;
}

.nav-brand {
  flex: none;
  color: var(--primary-dark);
  font-size: 0.95rem;
  font-weight: 600;
  letter-spacing: 0.5px;
  white-space: nowrap;
}

.nav-brand:hover {
  text-decoration: none;
}

.nav-links {
  display: flex;
  flex: 1;
  gap: 18px;
  overflow-x: auto;
  scrollbar-width: none;
}

.nav-links::-webkit-scrollbar {
  display: none;
}

.nav-links a {
  flex: none;
  color: var(--text-soft);
  font-size: 0.9rem;
  white-space: nowrap;
}

.nav-links a:hover {
  color: var(--primary);
  text-decoration: none;
}

.nav-user {
  display: flex;
  flex: none;
  align-items: center;
  gap: 8px;
}

.nav-user a {
  font-size: 0.85rem;
  white-space: nowrap;
}

.nav-qq {
  padding: 4px 12px;
  border-radius: 999px;
  background: #12b7f5;
  color: #fff;
  font-weight: 600;
}

.nav-qq:hover {
  background: #0aa5df;
  text-decoration: none;
}

.nav-login {
  padding: 4px 12px;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--primary-dark);
}

.nav-login:hover {
  border-color: var(--primary);
  text-decoration: none;
}

.nav-register {
  padding: 4px 12px;
  border-radius: 999px;
  background: var(--primary);
  color: #fff;
  font-weight: 600;
}

.nav-register:hover {
  background: var(--primary-dark);
  text-decoration: none;
}

/* 绑定 QQ 提示 */
.bind-tip {
  background: rgba(30, 111, 255, 0.08);
  border-bottom: 1px solid var(--border);
  color: var(--text);
  font-size: 0.85rem;
}

.bind-tip[hidden] {
  display: none;
}

.bind-tip-inner {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 8px 20px;
}

.bind-tip-text {
  flex: 1;
  min-width: 0;
}

.bind-tip-link {
  flex: none;
  color: var(--primary);
  font-weight: 600;
  white-space: nowrap;
}

.bind-tip-close {
  flex: none;
  width: 24px;
  height: 24px;
  padding: 0;
  border: 0;
  border-radius: 50%;
  background: transparent;
  color: var(--text-soft);
  font-size: 1.1rem;
  line-height: 1;
  cursor: pointer;
}

.bind-tip-close:hover {
  background: rgba(15, 23, 42, 0.08);
}

/* ====== 顶部 Hero ====== */
.hero {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
  color: #fff;
  padding: 28px 0 24px;
  text-align: center;
}

.hero h1 {
  font-size: clamp(1.3rem, 5.4vw, 2.25rem);
  font-weight: 700;
  letter-spacing: 0.5px;
  line-height: 1.4;
  margin-bottom: 8px;
  text-wrap: balance;
}

.hero .subtitle {
  font-size: clamp(0.95rem, 2.4vw, 1.05rem);
  opacity: 0.92;
}

.hero .subtitle .dot {
  white-space: nowrap;
}

/* ====== 主体区 ====== */
.main { padding: 20px 0 48px; }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 24px 20px;
  margin-bottom: 20px;
  box-shadow: var(--shadow);
}

.card h2 {
  font-size: 1.15rem;
  font-weight: 600;
  margin-bottom: 14px;
  color: var(--primary-dark);
  display: flex;
  align-items: center;
  gap: 8px;
}

.card h2::before {
  content: "";
  display: inline-block;
  width: 4px;
  height: 18px;
  background: var(--primary);
  border-radius: 2px;
}

.card p { color: var(--text-soft); margin-bottom: 10px; }
.card p:last-child { margin-bottom: 0; }

/* 标题 + 二维码 */
.hero-inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
  text-align: center;
}

.hero-copy {
  min-width: 0;
}

.hero-qr {
  display: flex;
  flex: none;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  padding: 8px 8px 6px;
  background: #fff;
  border-radius: 12px;
  box-shadow: 0 6px 18px rgba(2, 22, 60, 0.18);
}

.hero-qr img {
  display: block;
  width: 96px;
  height: 96px;
  border-radius: 6px;
  image-rendering: pixelated;
}

.hero-qr span {
  color: #1f2937;
  font-size: 0.72rem;
  line-height: 1.2;
  white-space: nowrap;
}

.hero-qr b {
  color: var(--primary);
}

/* ====== 链接按钮组 ====== */
.links {
  display: grid;
  grid-template-columns: 1fr;
  gap: 12px;
}

.link-item {
  display: block;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--card);
  color: var(--text);
  transition: border-color 0.2s, transform 0.1s;
}

.link-item:hover {
  border-color: var(--primary);
  text-decoration: none;
  transform: translateY(-1px);
}

.link-item .label {
  font-weight: 600;
  color: var(--primary-dark);
  display: block;
  margin-bottom: 4px;
}

.link-item .desc {
  font-size: 0.88rem;
  color: var(--text-soft);
}

.link-item .arrow {
  float: right;
  color: var(--primary);
  font-weight: 700;
}

/* ====== 投稿信息 ====== */
.contact-line {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin: 8px 0;
}

.contact-line .key {
  color: var(--text-soft);
  font-size: 0.92rem;
}

.email {
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  background: rgba(30, 111, 255, 0.08);
  padding: 2px 8px;
  border-radius: 4px;
  color: var(--primary-dark);
  font-size: 0.95rem;
}

/* ====== 页脚 ====== */
.footer {
  text-align: center;
  padding: 24px 20px;
  color: var(--text-soft);
  font-size: 0.85rem;
  border-top: 1px solid var(--border);
}

/* ====== 响应式：>=640px 双栏 ====== */
@media (min-width: 640px) {
  .hero { padding: 28px 0 24px; }
  .main { padding: 20px 0 48px; }
  .card { padding: 28px 28px; }
  .links {
    grid-template-columns: 1fr 1fr;
  }
}

@media (min-width: 900px) {
  body { font-size: 17px; }
  .hero { padding: 20px 0 16px; }
  .hero-inner {
    flex-direction: row;
    justify-content: center;
    gap: 28px;
    text-align: left;
  }
  .hero-qr img { width: 96px; height: 96px; }
}

/* ====== 活动公告 / 教研速递 ====== */
.channels {
  display: grid;
  gap: 16px;
  margin-bottom: 16px;
}

.channels .card {
  padding: 16px 18px;
}

.channels .panel-head {
  margin-bottom: 8px;
}

.channels .feed li {
  padding: 5px 0;
}

@media (min-width: 900px) {
  .channels {
    grid-template-columns: 1fr 1fr;
  }
}

/* ====== 社区动态（二维码下方） ====== */
.community {
  display: grid;
  gap: 16px;
  margin-bottom: 16px;
}

.panel-users {
  padding: 18px 20px;
}

.panel {
  margin-bottom: 0;
}

.panel-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 12px;
}

.panel-head h2 {
  margin-bottom: 0;
}

.more {
  flex: none;
  font-size: 0.8rem;
  color: var(--text-soft);
  white-space: nowrap;
}

.more:hover {
  color: var(--primary);
  text-decoration: none;
}

.panel-empty {
  color: var(--text-soft);
  font-size: 0.9rem;
  padding: 6px 0;
}

/* 活跃用户 */
.user-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 14px 8px;
}

.user {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 3px;
  min-width: 0;
  color: var(--text);
  text-align: center;
}

.user:hover {
  text-decoration: none;
}

.user:hover .user-name {
  color: var(--primary);
}

.user-avatar {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: clamp(36px, 9vw, 48px);
  height: clamp(36px, 9vw, 48px);
  border: 2px solid var(--border);
  border-radius: 50%;
  overflow: hidden;
  background: rgba(30, 111, 255, 0.08);
}

.user-avatar img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.avatar-fallback {
  font-size: 1rem;
  font-weight: 600;
  color: var(--primary);
}

.user-name {
  display: -webkit-box;
  height: 2.8em;
  max-width: 100%;
  overflow: hidden;
  font-size: 0.8rem;
  line-height: 1.3;
  -webkit-box-orient: vertical;
  -webkit-line-clamp: 2;
}

.user-meta {
  font-size: 0.72rem;
  color: var(--text-soft);
}

/* 日志 / 主题列表 */
.feed {
  list-style: none;
}

.feed li {
  padding: 10px 0;
  border-bottom: 1px dashed var(--border);
}

.feed li:first-child {
  padding-top: 0;
}

.feed li:last-child {
  padding-bottom: 0;
  border-bottom: 0;
}

.feed-title {
  display: -webkit-box;
  overflow: hidden;
  color: var(--text);
  font-size: 0.95rem;
  font-weight: 500;
  line-height: 1.5;
  -webkit-box-orient: vertical;
  -webkit-line-clamp: 2;
}

.feed-title:hover {
  color: var(--primary);
  text-decoration: none;
}

.feed-meta {
  margin-top: 4px;
  font-size: 0.78rem;
  color: var(--text-soft);
}

/* 公告 / 速递：标题和日期一行，标题超长省略 */
.feed-row {
  display: flex;
  align-items: baseline;
  gap: 10px;
}

.feed-row .feed-title {
  display: block;
  flex: 1;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  -webkit-line-clamp: unset;
}

.feed-date {
  flex: none;
  font-size: 0.78rem;
  color: var(--text-soft);
  white-space: nowrap;
}

@media (min-width: 900px) {
  .community {
    grid-template-columns: 1fr 1fr;
  }

  .panel-users {
    grid-column: 1 / -1;
  }

  .user-grid {
    grid-template-columns: repeat(10, minmax(0, 1fr));
    gap: 12px 6px;
  }

  .user-avatar {
    width: 44px;
    height: 44px;
  }

  .user-name {
    height: 1.5em;
    font-size: 0.74rem;
    -webkit-line-clamp: 1;
  }

  .user-meta {
    font-size: 0.68rem;
  }
}

@media (max-width: 639px) {
  .hero .subtitle > span {
    display: block;
  }

  .hero .subtitle .dot {
    display: none;
  }

  .nav-inner {
    gap: 12px;
    height: 44px;
  }

  .nav-brand,
  .nav-register {
    display: none;
  }

  .nav-links {
    gap: 14px;
  }
}