/* 2512 班 — 主题变量 */
:root {
  /* 纸感底色（暖白，非纯白） */
  --paper: #f6f3ec;
  --paper-deep: #efeade;
  --ink: #26241f;          /* 近黑墨色 */
  --ink-soft: #55524a;
  --ink-faint: #8a8578;
  --accent: #a4342a;       /* 朱砂红 —— 印章/重点 */
  --accent-deep: #7d2620;
  --gold: #9a7b3f;         /* 旧金 —— 细节点缀 */
  --line: #d8d2c2;         /* 分隔线 */

  --serif: "Noto Serif SC", "Anthropic Serif", "Songti SC", serif;
  --sans: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --wenkai: "LXGW WenKai", "Noto Serif SC", serif;
  --anth-serif: "Anthropic Serif", "Noto Serif SC", serif;
  --anth-mono: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, monospace;

  --max-w: 980px;
  --pad: clamp(1.2rem, 4vw, 2.5rem);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  /* 纸张噪点纹理 */
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='140' height='140'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.035 0'/%3E%3C/filter%3E%3Crect width='140' height='140' filter='url(%23n)'/%3E%3C/svg%3E");
}

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

::selection { background: rgba(164, 52, 42, 0.18); }

/* ---------- 版式骨架 ---------- */

.wrap {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--pad);
}

.site-header {
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: blur(6px);
  position: sticky;
  top: 0;
  z-index: 50;
}

.site-header .wrap {
  display: flex;
  align-items: baseline;
  gap: 1.5rem;
  padding-top: 0.9rem;
  padding-bottom: 0.9rem;
  flex-wrap: wrap;
}

.brand {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 1.35rem;
  letter-spacing: 0.06em;
}
.brand .num {
  font-family: var(--anth-serif);
  color: var(--accent);
}
.brand .space {
  font-size: 0.72em;
  color: var(--ink-faint);
  letter-spacing: 0.28em;
  margin-left: 0.3em;
}

.nav { display: flex; gap: 1.4rem; margin-left: auto; flex-wrap: wrap; }
.nav a {
  font-size: 0.92rem;
  color: var(--ink-soft);
  letter-spacing: 0.12em;
  transition: color 0.15s;
  position: relative;
}
.nav a:hover { color: var(--accent); }
.nav a[aria-current="page"] { color: var(--ink); }
.nav a[aria-current="page"]::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -0.55em;
  height: 2px;
  background: var(--accent);
}

.site-footer {
  border-top: 1px solid var(--line);
  margin-top: 5rem;
  padding: 2rem 0 3rem;
  color: var(--ink-faint);
  font-size: 0.85rem;
}
.site-footer .wrap {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
}

/* ---------- 通用组件 ---------- */

.section { margin-top: 4.5rem; }

.sec-head { display: flex; align-items: baseline; gap: 0.9rem; margin-bottom: 1.6rem; }
.sec-head h2 {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 1.5rem;
  letter-spacing: 0.08em;
}
.sec-head .en {
  font-family: var(--anth-serif);
  font-style: italic;
  color: var(--ink-faint);
  font-size: 0.9rem;
  letter-spacing: 0.04em;
}
.sec-head::after {
  content: "";
  flex: 1;
  height: 1px;
  background: linear-gradient(to right, var(--line), transparent);
}

/* 朱砂印章式标签 */
.stamp {
  display: inline-block;
  font-family: var(--serif);
  font-weight: 700;
  font-size: 0.78rem;
  color: #f6f3ec;
  background: var(--accent);
  padding: 0.15em 0.5em;
  letter-spacing: 0.2em;
  border-radius: 2px;
  transform: rotate(-1.5deg);
}

.btn {
  display: inline-block;
  font-family: var(--sans);
  font-size: 0.92rem;
  letter-spacing: 0.1em;
  padding: 0.55em 1.5em;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  cursor: pointer;
  transition: all 0.18s;
}
.btn:hover { background: var(--ink); color: var(--paper); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.primary:hover { background: var(--accent-deep, #7d2620); border-color: var(--accent-deep, #7d2620); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }

input[type="text"], input[type="email"], textarea, select {
  font-family: var(--sans);
  font-size: 0.95rem;
  color: var(--ink);
  background: #fffef9;
  border: 1px solid var(--line);
  padding: 0.6em 0.8em;
  width: 100%;
  transition: border-color 0.15s;
}
input:focus, textarea:focus, select:focus {
  outline: none;
  border-color: var(--gold);
}
textarea { resize: vertical; min-height: 6.5em; }

.field { margin-bottom: 1rem; }
.field label {
  display: block;
  font-size: 0.82rem;
  letter-spacing: 0.15em;
  color: var(--ink-soft);
  margin-bottom: 0.35em;
}
.field .hint { font-size: 0.78rem; color: var(--ink-faint); }

.form-ok {
  display: none;
  margin-top: 0.8rem;
  padding: 0.7em 1em;
  border-left: 3px solid var(--accent);
  background: var(--paper-deep);
  font-size: 0.92rem;
}
.form-ok.show { display: block; }
.form-err { color: var(--accent); font-size: 0.85rem; margin-top: 0.6rem; display: none; }
.form-err.show { display: block; }

/* ---------- 首页 Hero ---------- */

.hero { padding: 6.5rem 0 5rem; position: relative; overflow: hidden; }

.hero h1 {
  font-family: var(--serif);
  font-weight: 700;
  font-size: clamp(2.6rem, 7vw, 4.6rem);
  line-height: 1.18;
  letter-spacing: 0.04em;
  max-width: 14em;
}
.hero h1 .yr {
  font-family: var(--anth-serif);
  font-style: italic;
  font-weight: 400;
  color: var(--accent);
  font-size: 0.55em;
  display: block;
  letter-spacing: 0.02em;
  margin-top: 0.4em;
}
.hero p.sub {
  margin-top: 1.8rem;
  font-family: var(--wenkai);
  font-size: 1.12rem;
  color: var(--ink-soft);
  max-width: 34em;
}
.hero .cta { margin-top: 2.6rem; display: flex; gap: 1rem; flex-wrap: wrap; }

/* 装饰：背景超大 2512 数字 */
.hero .bg-num {
  position: absolute;
  right: -0.06em;
  bottom: -0.32em;
  font-family: var(--anth-serif);
  font-style: italic;
  font-size: clamp(11rem, 26vw, 19rem);
  line-height: 1;
  color: transparent;
  -webkit-text-stroke: 1px var(--line);
  user-select: none;
  pointer-events: none;
  z-index: -1;
}

/* ---------- 时间线 ---------- */

.tl { position: relative; padding-left: 2.2rem; }
.tl::before {
  content: "";
  position: absolute;
  left: 0.45rem; top: 0.4rem; bottom: 0.4rem;
  width: 1px;
  background: var(--line);
}
.tl-item { position: relative; padding-bottom: 2.2rem; }
.tl-item:last-child { padding-bottom: 0; }
.tl-item::before {
  content: "";
  position: absolute;
  left: calc(-2.2rem + 0.09rem); top: 0.5rem;
  width: 9px; height: 9px;
  border-radius: 50%;
  background: var(--paper);
  border: 2px solid var(--accent);
}
.tl-date {
  font-family: var(--anth-serif);
  font-style: italic;
  font-size: 0.88rem;
  color: var(--accent);
  letter-spacing: 0.04em;
}
.tl-title {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 1.12rem;
  margin: 0.15em 0 0.3em;
}
.tl-body { color: var(--ink-soft); font-size: 0.96rem; max-width: 42em; }

/* ---------- 照片墙 ---------- */

.photos { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 1.1rem; }
.ph {
  position: relative;
  aspect-ratio: 4 / 3;
  background: var(--paper-deep);
  border: 1px solid var(--line);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--ink-faint);
  font-size: 0.82rem;
  overflow: hidden;
}
.ph img { width: 100%; height: 100%; object-fit: cover; display: block; }
.ph .cap {
  position: absolute;
  left: 0; right: 0; bottom: 0;
  padding: 1.4em 0.8em 0.5em;
  background: linear-gradient(transparent, rgba(20, 18, 14, 0.65));
  color: #f4f1e8;
  font-size: 0.8rem;
  letter-spacing: 0.06em;
}

/* ---------- 留言墙 ---------- */

.msgs { display: grid; gap: 0.9rem; }
.msg {
  background: #fffef9;
  border: 1px solid var(--line);
  padding: 1rem 1.2rem 0.85rem;
  position: relative;
}
.msg .meta {
  display: flex;
  justify-content: space-between;
  font-size: 0.8rem;
  color: var(--ink-faint);
  margin-bottom: 0.4em;
}
.msg .meta .who {
  font-family: var(--wenkai);
  color: var(--ink-soft);
  font-size: 0.92rem;
}
.msg .body { font-size: 0.95rem; white-space: pre-wrap; word-break: break-word; }

/* ---------- 讨论区（短轮询） ---------- */

#chat-box {
  height: 340px;
  overflow-y: auto;
  border: 1px solid var(--line);
  background: #fffef9;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
}
.chat-line { font-size: 0.94rem; }
.chat-line .t { font-family: var(--anth-serif); font-style: italic; color: var(--ink-faint); font-size: 0.75rem; margin-right: 0.5em; }
.chat-line .who { font-family: var(--wenkai); color: var(--accent); margin-right: 0.4em; }
.chat-form { display: flex; gap: 0.6rem; margin-top: 0.8rem; }
.chat-form input[name="author"] { width: 9em; flex: none; }
.chat-form input[name="body"] { flex: 1; }
.chat-status { font-size: 0.75rem; color: var(--ink-faint); margin-top: 0.4rem; letter-spacing: 0.08em; }

/* ---------- 同学名单（按字母分组） ---------- */

.letter-group {
  margin-bottom: 3.2rem;
  opacity: 0;
  animation: letter-group-in 0.7s cubic-bezier(0.22, 0.68, 0.26, 1) forwards;
  animation-delay: calc(var(--group-i, 0) * 0.06s);
}

.letter-group .letter {
  font-family: var(--anth-serif);
  font-style: italic;
  font-size: clamp(3.2rem, 8vw, 5.5rem);
  line-height: 1;
  letter-spacing: -0.02em;
  color: transparent;
  -webkit-text-stroke: 1.5px var(--line);
  margin-bottom: 0.5rem;
  user-select: none;
}

.letter-group .names {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(clamp(5.5rem, 15vw, 7.5rem), 1fr));
  gap: clamp(1.2rem, 3vw, 2rem);
}

.letter-group .name {
  font-family: "LXGW WenKai", var(--serif);
  font-size: clamp(1.05rem, 2.5vw, 1.3rem);
  font-weight: 500;
  letter-spacing: 0.12em;
  color: var(--ink);
  text-align: center;
  padding: 0.6em 0.3em;
  position: relative;
  display: block;
  transition: all 0.32s cubic-bezier(0.25, 0.6, 0.3, 1);
}

.letter-group .name::before {
  content: "";
  position: absolute;
  left: 50%; bottom: 0.2em;
  width: 0; height: 1.5px;
  background: var(--accent);
  transform: translateX(-50%);
  transition: width 0.32s cubic-bezier(0.25, 0.6, 0.3, 1);
}

.letter-group .name:hover {
  color: var(--accent);
  transform: translateY(-2px);
}

.letter-group .name:hover::before {
  width: 2.2em;
}

@keyframes letter-group-in {
  from { opacity: 0; transform: translateY(18px); }
  to { opacity: 1; transform: none; }
}

/* ---------- 移动端 ---------- */

@media (max-width: 640px) {
  .hero { padding: 4rem 0 3.2rem; }
  .nav { margin-left: 0; gap: 1rem; }
  .section { margin-top: 3.2rem; }
}