/* 黑板粉笔板书页面（web-v4）：深灰绿黑板 + 粉笔质感，公式仍走 KaTeX 默认字形。
   粉笔纹理：两层细噪点（data-URI 的 feTurbulence SVG），叠加在黑板底色上。 */
@font-face {
  font-family: "HanziPen SC";
  font-style: normal;
  font-weight: 400;
  font-display: swap;
  src: url("/fonts/maoken-ying-bi-kai-shu-j-0.20.woff2") format("woff2");
}

:root {
  color-scheme: dark;
  --board: #26413a;            /* 黑板底色 */
  --board-deep: #1d322d;       /* 边缘加深 */
  --chalk: #f2efe3;            /* 粉笔白（略暖） */
  --chalk-dim: #b9c3b5;        /* 粉笔灰绿（行号/副文本） */
  --chalk-yellow: #ffe08a;     /* 高亮粉笔黄 */
  --chalk-purple: #d8b8f0;     /* 答案与标注粉笔紫 */
  --chalk-blue: #a9d6ff;       /* 标题与下划线粉笔蓝 */
  --chalk-border: rgba(242, 239, 227, .14);
}
body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(1200px 600px at 50% -10%, #2e4f46, transparent 60%),
    linear-gradient(180deg, var(--board) 0%, var(--board-deep) 100%);
  color: var(--chalk);
  font-family: system-ui, -apple-system, sans-serif;
}
/* 粉笔颗粒噪点（整页覆盖，可点穿透） */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  opacity: .5;
  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='.9' numOctaves='2'/%3E%3CfeColorMatrix values='0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 .05 0'/%3E%3C/filter%3E%3Crect width='140' height='140' filter='url(%23n)'/%3E%3C/svg%3E");
}
header, main { position: relative; z-index: 1; }
header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  max-width: 820px;
  margin: 0 auto;
  padding: 20px 16px 8px;
}
h1 { margin: 0; font-size: 18px; font-weight: 600; color: var(--chalk); }
a.back { color: var(--chalk-blue); font-size: 14px; }
main { max-width: 820px; margin: 0 auto; padding: 0 16px 48px; }
textarea {
  width: 100%;
  box-sizing: border-box;
  min-height: 72px;
  background: rgba(0, 0, 0, .25);
  color: var(--chalk);
  border: 1px solid var(--chalk-border);
  border-radius: 6px;
  padding: 10px;
  font-size: 15px;
  line-height: 1.6;
}
textarea::placeholder { color: rgba(242, 239, 227, .4); }
.actions { margin: 10px 0; }
button {
  border: 1px solid rgba(242, 239, 227, .3);
  background: rgba(255, 255, 255, .08);
  color: var(--chalk);
  border-radius: 6px;
  padding: 8px 16px;
  font-size: 14px;
  cursor: pointer;
  margin-right: 8px;
}
button:hover:not(:disabled) { background: rgba(255, 255, 255, .16); }
button:disabled { opacity: .4; cursor: default; }
/* 黑板板面：比页面底色更深的墨绿，细边框 + 粉笔灰的边沿 */
#paper {
  box-sizing: border-box;
  min-height: 260px;
  padding: 20px 22px;
  background: linear-gradient(180deg, #223a33, #1c2f29);
  border: 1px solid var(--chalk-border);
  border-radius: 4px;
  box-shadow: 0 2px 18px rgba(0, 0, 0, .35), inset 0 0 60px rgba(0, 0, 0, .28);
}
#paper:empty { display: none; }
#subtitle {
  margin-top: 14px;
  font-size: 15px;
  line-height: 1.6;
  color: var(--chalk-dim);
  min-height: 24px;
}
#status { margin-top: 6px; font-size: 12px; color: rgba(242, 239, 227, .45); min-height: 16px; }
#controls, #options { margin-top: 12px; }
.hidden { display: none; }

/* —— 板书行 —— */
.op { position: relative; margin: 8px 0; max-width: 100%; overflow-x: auto; padding: 3px 0 7px; }
.op-body { position: relative; display: inline-block; }
.op-title { margin-top: 12px; }
.op canvas { display: block; }
.writing-hand {
  position: absolute;
  z-index: 5;
  top: 0;
  left: 0;
  width: 42px;
  height: auto;
  opacity: 0;
  pointer-events: none;
  user-select: none;
  transform: translate3d(-100px, -100px, 0);
  transform-origin: 0 0;
  transition: opacity 70ms linear;
  will-change: transform, opacity;
}
.writing-hand.is-active { opacity: .96; }
.op-write { font-size: 19px; }
.op-write .formula { min-width: 0; }
.op-answer .formula-fallback { color: var(--chalk-purple); }
.op.marked { outline: none; }

/* —— KaTeX 公式：默认字形，粉笔白 —— */
.katex { color: var(--chalk); }
.katex-display { margin: 0; }
.op-write .katex, .op-answer .katex { font-size: 1.05em; }
.op-answer .katex { color: var(--chalk-purple); }
.formula-mixed { font-family: "HanziPen SC"; line-height: 1.4; display: block; overflow-wrap: anywhere; }
.formula-mixed .katex { color: inherit; }
.op-problem .op-body { display: block; }
.problem-static { font-family: system-ui, -apple-system, sans-serif; line-height: 1.6; overflow-x: auto; }
.problem-static .katex { color: inherit; }

/* —— 手绘几何效果（线色改为粉笔系） —— */
.deco { position: absolute; pointer-events: none; }
.deco svg, .deco canvas { display: block; width: 100%; height: 100%; }
.deco path { fill: none; stroke-linecap: round; stroke-linejoin: round; stroke-dasharray: 100000; stroke-dashoffset: 100000; vector-effect: non-scaling-stroke; }
.deco .deco-start { stroke-width: calc(var(--deco-stroke, 2px) + .55px); opacity: .72; }
/* perfect-freehand 手绘轮廓：fill 多边形；JS 逐帧替换中心线前缀，不做整形淡入 */
.deco .deco-fill { stroke: none; }
.deco-underline .deco-fill { fill: var(--chalk-blue); }
.deco-circle .deco-fill, .deco-mark .deco-fill { fill: var(--chalk-purple); }
.deco-underline path { stroke: var(--chalk-blue); stroke-width: var(--deco-stroke, 2.2px); }
.deco-circle path, .deco-mark path { stroke: var(--chalk-purple); stroke-width: var(--deco-stroke, 2.4px); }
.note { color: var(--chalk-purple); font-weight: 700; margin-left: 6px; font-size: 15px; font-family: "HanziPen SC"; }

@media (prefers-reduced-motion: reduce) {
  .writing-hand { transition: none; }
}
@media (max-width: 600px) {
  header { flex-wrap: wrap; }
  #paper { padding: 16px; }
  button { margin-bottom: 6px; }
}
#options { display: flex; flex-wrap: wrap; gap: 8px; }
#options.hidden { display: none; }
#options button { max-width: 100%; min-width: 0; margin: 0; text-align: left; overflow-x: auto; }
label[for="q"] { display: block; margin: 12px 0 8px; }
#examples { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 8px; }
#examples button { margin: 0; }
#board-text { margin-top: 12px; }
#transcript li { margin: 8px 0; overflow-x: auto; }
button:focus-visible, summary:focus-visible, textarea:focus-visible, input:focus-visible { outline: 2px solid var(--chalk-blue); outline-offset: 3px; }
#status { color: var(--chalk-dim); font-size: 14px; }