:root {
  --bg: #f6f7f9;
  --card: #ffffff;
  --ink: #1a1d21;
  --ink-2: #5b6470;
  --ink-3: #8b95a1;
  --line: #e3e7ec;
  --brand: #2563eb;
  --brand-soft: #eaf1ff;
  --ok: #0f9960;
  --ok-soft: #e6f6ee;
  --bad: #d64545;
  --bad-soft: #fdecec;
  --radius: 14px;
  --safe-b: env(safe-area-inset-bottom, 0px);
  --safe-t: env(safe-area-inset-top, 0px);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14171a;
    --card: #1d2126;
    --ink: #e9edf2;
    --ink-2: #a4b0bd;
    --ink-3: #78838f;
    --line: #2c333a;
    --brand: #5b9bff;
    --brand-soft: #1b2a44;
    --ok: #4ade80;
    --ok-soft: #14302180;
    --bad: #f87171;
    --bad-soft: #3a1d1d80;
  }
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }

html, body {
  margin: 0; padding: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.65 -apple-system, BlinkMacSystemFont, "PingFang SC", "Helvetica Neue", "Microsoft YaHei", sans-serif;
  overscroll-behavior-y: none;
}

.hidden { display: none !important; }

/* ---------- 登录 ---------- */

#login {
  min-height: 100dvh;
  display: flex; align-items: center; justify-content: center;
  padding: 24px;
}
.login-box {
  width: 100%; max-width: 340px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 32px 24px;
  text-align: center;
}
.logo { font-size: 26px; font-weight: 600; letter-spacing: 1px; }
.login-hint { color: var(--ink-2); font-size: 15px; margin: 8px 0 22px; }

input, textarea {
  width: 100%;
  font-size: 16px;
  font-family: inherit;
  color: var(--ink);
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 13px 14px;
}
input:focus, textarea:focus { outline: 2px solid var(--brand); outline-offset: -1px; }
textarea { resize: vertical; }

.btn-primary {
  width: 100%;
  margin-top: 14px;
  padding: 14px;
  font-size: 17px;
  font-weight: 500;
  color: #fff;
  background: var(--brand);
  border: 0; border-radius: 10px;
  cursor: pointer;
}
.btn-primary:active { filter: brightness(0.92); }
.btn-primary:disabled { opacity: .55; }
.btn-primary.big { margin-top: 18px; padding: 17px; font-size: 18px; }

.err { color: var(--bad); font-size: 14px; margin-top: 10px; min-height: 20px; }

/* ---------- 主框架 ---------- */

.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; gap: 6px;
  padding: calc(var(--safe-t) + 10px) 14px 10px;
  background: var(--bg);
  border-bottom: 1px solid var(--line);
}
.tab {
  flex: 0 0 auto;
  padding: 8px 16px;
  font-size: 15px;
  font-family: inherit;
  color: var(--ink-2);
  background: transparent;
  border: 0; border-radius: 20px;
  cursor: pointer;
}
.tab.active { color: var(--brand); background: var(--brand-soft); font-weight: 500; }

.view { padding: 16px 14px calc(var(--safe-b) + 28px); max-width: 760px; margin: 0 auto; }

/* ---------- 模式 / 学科 ---------- */

.modes { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; }
.mode {
  display: flex; flex-direction: column; gap: 3px;
  padding: 13px 8px;
  font-family: inherit;
  text-align: center;
  color: var(--ink-2);
  background: var(--card);
  border: 1.5px solid var(--line);
  border-radius: 12px;
  cursor: pointer;
}
.mode b { font-size: 16px; font-weight: 600; color: var(--ink); }
.mode span { font-size: 11.5px; line-height: 1.35; color: var(--ink-3); }
.mode.active { border-color: var(--brand); background: var(--brand-soft); }
.mode.active b { color: var(--brand); }

.subjects {
  display: flex; gap: 7px; flex-wrap: wrap;
  margin-top: 14px;
}
.subj {
  padding: 7px 15px;
  font-size: 14.5px;
  font-family: inherit;
  color: var(--ink-2);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 18px;
  cursor: pointer;
}
.subj.active { color: #fff; background: var(--brand); border-color: var(--brand); }

/* ---------- 图片 ---------- */

.thumbs { display: flex; gap: 9px; flex-wrap: wrap; margin-top: 14px; }
.thumbs:empty { margin-top: 0; }
.thumb { position: relative; width: 82px; height: 82px; }
.thumb img {
  width: 100%; height: 100%;
  object-fit: cover;
  border-radius: 10px;
  border: 1px solid var(--line);
}
.thumb button {
  position: absolute; top: -7px; right: -7px;
  width: 23px; height: 23px;
  font-size: 15px; line-height: 1;
  color: #fff; background: #333;
  border: 2px solid var(--card); border-radius: 50%;
  cursor: pointer;
}

.pickers { display: flex; gap: 10px; margin-top: 14px; }
.btn-pick {
  flex: 1;
  padding: 15px;
  font-size: 16px;
  text-align: center;
  color: var(--brand);
  background: var(--card);
  border: 1.5px dashed var(--line);
  border-radius: 12px;
  cursor: pointer;
}
.btn-pick:active { background: var(--brand-soft); }

#q { margin-top: 14px; }

/* ---------- 对话 ---------- */

.chat-head {
  display: flex; align-items: center; gap: 12px;
  margin-bottom: 12px;
}
.link {
  padding: 6px 0;
  font-size: 15px; font-family: inherit;
  color: var(--brand); background: none; border: 0; cursor: pointer;
}
.chat-title {
  font-size: 14px; color: var(--ink-3);
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}

.chat { display: flex; flex-direction: column; gap: 16px; }

.bubble-me {
  align-self: flex-end;
  max-width: 85%;
  padding: 11px 15px;
  color: #fff; background: var(--brand);
  border-radius: 16px 16px 4px 16px;
  white-space: pre-wrap;
}
.bubble-me .imgs { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 8px; }
.bubble-me .imgs img { width: 74px; height: 74px; object-fit: cover; border-radius: 8px; }

.bubble-ai {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 4px 16px 16px 16px;
  padding: 16px 17px;
  overflow-wrap: anywhere;
}
.bubble-ai h1, .bubble-ai h2, .bubble-ai h3 {
  font-size: 17px; font-weight: 600; margin: 18px 0 8px;
}
.bubble-ai h1:first-child, .bubble-ai h2:first-child, .bubble-ai h3:first-child { margin-top: 0; }
.bubble-ai p { margin: 10px 0; }
.bubble-ai p:first-child { margin-top: 0; }
.bubble-ai p:last-child { margin-bottom: 0; }
.bubble-ai ul, .bubble-ai ol { margin: 10px 0; padding-left: 22px; }
.bubble-ai li { margin: 5px 0; }
.bubble-ai hr { border: 0; border-top: 1px solid var(--line); margin: 16px 0; }
.bubble-ai code {
  font-size: 14px;
  background: var(--bg);
  padding: 2px 5px; border-radius: 4px;
}
.bubble-ai pre {
  background: var(--bg); padding: 12px;
  border-radius: 8px; overflow-x: auto;
}
.bubble-ai pre code { background: none; padding: 0; }
.bubble-ai table { border-collapse: collapse; width: 100%; margin: 12px 0; font-size: 15px; }
.bubble-ai th, .bubble-ai td { border: 1px solid var(--line); padding: 7px 10px; text-align: left; }
.bubble-ai blockquote {
  margin: 12px 0; padding: 2px 14px;
  border-left: 3px solid var(--line); color: var(--ink-2);
}
.bubble-ai .katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

.meta { font-size: 12px; color: var(--ink-3); margin-top: 10px; }

/* 等待动画 */
.waiting {
  display: flex; align-items: center; gap: 11px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 4px 16px 16px 16px;
  padding: 16px 17px;
  color: var(--ink-2);
}
.spin {
  width: 17px; height: 17px; flex: 0 0 auto;
  border: 2.5px solid var(--line);
  border-top-color: var(--brand);
  border-radius: 50%;
  animation: spin .8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }
.waiting .t { font-variant-numeric: tabular-nums; color: var(--ink-3); font-size: 13px; }

.followup {
  position: sticky; bottom: 0;
  display: flex; gap: 8px;
  margin-top: 18px;
  padding: 10px 0 calc(var(--safe-b) + 10px);
  background: linear-gradient(to bottom, transparent, var(--bg) 22%);
}
.followup input { flex: 1; }
.btn-send {
  padding: 0 20px;
  font-size: 16px; font-family: inherit;
  color: #fff; background: var(--brand);
  border: 0; border-radius: 10px; cursor: pointer;
}
.btn-send:disabled { opacity: .5; }

/* ---------- 历史 ---------- */

.history { display: flex; flex-direction: column; gap: 9px; }
.hitem {
  display: flex; align-items: center; gap: 12px;
  padding: 14px 15px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  cursor: pointer;
}
.hitem .body { flex: 1; min-width: 0; }
.hitem .t {
  font-size: 15.5px;
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.hitem .s { font-size: 12.5px; color: var(--ink-3); margin-top: 3px; }
.hitem .del {
  flex: 0 0 auto;
  padding: 7px 10px;
  font-size: 13px; font-family: inherit;
  color: var(--ink-3); background: none;
  border: 1px solid var(--line); border-radius: 8px;
  cursor: pointer;
}
.empty { color: var(--ink-3); text-align: center; padding: 48px 20px; font-size: 15px; }