:root {
  --bg: #f6f7f9;
  --surface: #ffffff;
  --border: #e2e8f0;
  --text: #1e293b;
  --muted: #64748b;
  --accent: #3730a3;
  --accent-soft: #eef2ff;
  --notice-bg: #fefce8;
  --notice-border: #fde047;
  --notice-text: #854d0e;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  font-size: 15px;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.container {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 20px;
}

header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 18px 0;
}

.header-inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.brand h1 {
  margin: 0;
  font-size: 20px;
  font-weight: 700;
  letter-spacing: -0.01em;
}

.brand p {
  margin: 2px 0 0;
  font-size: 13px;
  color: var(--muted);
}

nav {
  display: flex;
  gap: 18px;
  font-size: 14px;
  font-weight: 500;
}

main {
  padding: 24px 0 48px;
}

.notice {
  background: var(--notice-bg);
  border: 1px solid var(--notice-border);
  color: var(--notice-text);
  border-radius: 8px;
  padding: 10px 14px;
  font-size: 13.5px;
  margin-bottom: 20px;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  overflow: hidden;
}

.thread-item {
  padding: 16px 20px;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
}

.thread-item:last-child {
  border-bottom: none;
}

.thread-title {
  margin: 0 0 6px;
  font-size: 16px;
  font-weight: 600;
}

.thread-excerpt {
  margin: 0 0 8px;
  font-size: 14px;
  color: #475569;
}

.meta {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  font-size: 12.5px;
  color: var(--muted);
}

.tag {
  background: var(--accent-soft);
  color: var(--accent);
  padding: 2px 8px;
  border-radius: 999px;
  font-weight: 500;
  font-size: 12px;
}

.reply-count {
  min-width: 64px;
  text-align: center;
  background: #f1f5f9;
  border-radius: 8px;
  padding: 6px 10px;
  font-size: 12.5px;
  color: var(--muted);
  flex-shrink: 0;
}

.reply-count strong {
  display: block;
  font-size: 15px;
  color: var(--text);
}

.breadcrumb {
  margin-bottom: 14px;
  font-size: 13.5px;
  color: var(--muted);
}

.post {
  padding: 20px 22px;
  border-bottom: 1px solid var(--border);
}

.post:last-child {
  border-bottom: none;
}

.post-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
  font-size: 13px;
  color: var(--muted);
}

.author {
  font-weight: 600;
  color: var(--text);
}

.math {
  font-family: "Times New Roman", Georgia, serif;
  font-style: italic;
}

code {
  background: #f1f5f9;
  padding: 2px 5px;
  border-radius: 4px;
  font-size: 13px;
}

footer {
  border-top: 1px solid var(--border);
  padding: 20px 0;
  font-size: 13px;
  color: var(--muted);
  text-align: center;
}