/* 课时讲解页 —— 只补 site.css 没有的部分 */
/* 顶栏是 sticky，锚点/scrollIntoView 必须留出它的高度，否则标题被压在导航下面 */
html { scroll-padding-top: 76px; }
main.learn { max-width: 1180px; margin: 0 auto; padding: 24px 18px 72px; }
.learn .page-head { margin: 4px 0 20px; }
.learn .page-head h1 { margin: 0 0 6px; font-size: clamp(23px, 3.6vw, 30px); letter-spacing: -.01em; }
.learn .page-head p { margin: 0; color: var(--ink-2); font-size: 15px; }

.picker { padding: 16px 18px; margin-bottom: 18px; }
.select-group { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 14px; }
.select-group label { display: block; font-weight: 650; font-size: 13.5px; margin-bottom: 7px; }
.select-group select {
  width: 100%; min-height: 44px; padding: 0 12px; font-size: 14.5px; color: var(--ink);
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius-sm, 8px);
}
.hint { margin: 12px 0 0; font-size: 13px; color: var(--ink-3); }

.split { display: grid; grid-template-columns: 320px minmax(0, 1fr); gap: 18px; align-items: start; }
@media (max-width: 860px) { .split { grid-template-columns: 1fr; } }

.lesson-list {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius, 12px);
  padding: 10px 8px; max-height: 78vh; overflow: auto; position: sticky; top: 14px;
}
@media (max-width: 860px) { .lesson-list { max-height: none; position: static; } }
.lesson-list .unit {
  font-size: 12.5px; font-weight: 700; color: var(--ink-3); letter-spacing: .02em;
  margin: 12px 8px 6px; padding-top: 8px; border-top: 1px solid var(--line);
}
.lesson-list .unit:first-child { border-top: 0; margin-top: 4px; }
.lesson-list button.lesson {
  display: block; width: 100%; text-align: left; padding: 9px 10px; margin: 1px 0;
  background: none; border: 0; border-radius: 8px; cursor: pointer;
  font-size: 14px; color: var(--ink); line-height: 1.45;
}
.lesson-list button.lesson:hover { background: var(--brand-soft); }
.lesson-list button.lesson.active { background: var(--brand); color: #fff; font-weight: 650; }
.lesson-list button.lesson .w { font-size: 11.5px; color: var(--ink-3); margin-left: 6px; }
.lesson-list button.lesson.active .w { color: #d9f0ec; }
.lesson-list .empty { color: var(--ink-3); font-size: 13.5px; padding: 12px; }

.reader {
  scroll-margin-top: 78px;
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius, 12px);
  padding: 26px 30px 34px; box-shadow: var(--shadow, 0 1px 2px rgba(0,0,0,.05)); min-height: 46vh;
}
@media (max-width: 560px) { .reader { padding: 20px 18px 26px; } }
.reader-empty h2 { margin: 6px 0 10px; font-size: 20px; }
.reader-empty p { color: var(--ink-2); font-size: 14.5px; line-height: 1.7; }
.reader-empty .cols { margin: 14px 0 0; padding-left: 20px; color: var(--ink-2); font-size: 14px; line-height: 1.9; }

.reader h1 { font-size: 24px; margin: 0 0 4px; letter-spacing: -.01em; }
.reader .meta { font-size: 12.5px; color: var(--ink-3); margin-bottom: 18px; }
.reader h2 {
  font-size: 17px; margin: 26px 0 10px; padding-left: 10px;
  border-left: 3px solid var(--brand); line-height: 1.4;
}
.reader h3 { font-size: 15px; margin: 18px 0 8px; color: var(--brand-ink); }
.reader p { margin: 0 0 12px; font-size: 15.5px; line-height: 1.85; color: var(--ink); }
.reader strong { font-weight: 700; }
.reader blockquote {
  margin: 10px 0 12px; padding: 12px 16px; background: #f5f7f9;
  border-left: 3px solid #cfd8e0; border-radius: 0 8px 8px 0;
  font-size: 15px; line-height: 1.8; color: #2a3540;
}
.reader blockquote p { margin: 0; font-size: inherit; }
.reader .cmp { background: none; border-left: 0; padding: 4px 0 4px 2px; }
.reader .cmp.bad { color: #a4342a; }
.reader .cmp.good { color: #12734f; }
.reader ul.check { list-style: none; padding-left: 0; margin: 8px 0 14px; }
.reader ul.check li {
  position: relative; padding: 6px 0 6px 26px; font-size: 15px; line-height: 1.7;
  border-bottom: 1px dashed var(--line);
}
.reader ul.check li::before {
  content: "☐"; position: absolute; left: 4px; color: var(--brand); font-size: 15px;
}
/* site.css 里 ol 被全局设成 grid（首页卡片网格用），讲解页必须重置成普通列表 */
.reader ol.steps-list { display: block; list-style: decimal outside; margin: 10px 0 16px; padding-left: 26px; }
.reader ol.steps-list li { display: list-item; list-style: decimal outside;
  font-size: 15.5px; line-height: 1.85; margin-bottom: 12px; padding-left: 4px;
}
.reader ol.steps-list li::marker { color: var(--brand); font-weight: 700; }
/* 规范根号：√ 后接被开方数，顶部用 border-top 画横线 */
.rad { white-space: nowrap; display: inline-block; line-height: 1.15; vertical-align: -0.02em; }
.rad .sq { display: inline-block; transform: scaleY(1.18) translateY(.02em); }
.rad .rd {
  display: inline-block; border-top: 1.5px solid currentColor;
  padding: .05em .16em 0 .1em; margin-left: -.04em;
}
.reader ul.dot { margin: 8px 0 14px; padding-left: 22px; }
.reader ul.dot li { font-size: 15.5px; line-height: 1.8; margin-bottom: 4px; }
.reader .navrow {
  display: flex; justify-content: space-between; gap: 12px;
  margin-top: 30px; padding-top: 16px; border-top: 1px solid var(--line);
}
.reader .navrow button {
  min-height: 40px; padding: 0 14px; font-size: 14px; cursor: pointer;
  background: var(--card); border: 1px solid var(--line); border-radius: 8px; color: var(--ink);
}
.reader .navrow button:hover { border-color: var(--brand); color: var(--brand-ink); }
.reader .navrow button:disabled { opacity: .45; cursor: not-allowed; }
.reader .src { margin-top: 14px; font-size: 12px; color: var(--ink-3); }

/* 规范分式：上下叠排 + 分数线 */
.frac { display: inline-flex; flex-direction: column; align-items: center;
  vertical-align: middle; margin: 0 .1em; font-size: .88em; line-height: 1.02;
  position: relative; top: -0.06em; }
.frac .num { display: block; border-bottom: 1.2px solid currentColor; padding: 0 .16em; }
.frac .den { display: block; padding: 0 .16em; }

/* 向量：字母正上方一条右箭头（自画线，不用字体 overline，离字母更近、长度随字母宽） */
.vec { position: relative; display: inline-block; line-height: 1; }
.vec::before {
  content: ""; position: absolute; left: 0; right: .08em; top: -.06em;
  border-top: 1px solid currentColor;
}
.vec::after {
  content: ""; position: absolute; right: -.04em; top: -.14em;
  border-left: .3em solid currentColor;
  border-top: .12em solid transparent;
  border-bottom: .12em solid transparent;
}

/* 根号内部的幂与分数（横线之内），字号缩一档避免顶穿根号横线 */
.rad .rd sup { font-size: .72em; vertical-align: .38em; line-height: 0; }
.rad .rd .frac { font-size: .78em; vertical-align: middle; margin: 0 .02em; }
.rad .rd .frac .num, .rad .rd .frac .den { font-size: inherit; }

/* 讲解目录的二级 tab：诊断讲解 / 试卷讲解 */
.subnav { display: flex; gap: 10px; margin: 0 0 16px; flex-wrap: wrap; }
.subnav .sub-link { display: flex; flex-direction: column; gap: 2px; padding: 10px 16px;
  border: 1px solid #d8e2e0; border-radius: 10px; background: #fff; color: #1d3b38;
  font-weight: 600; text-decoration: none; line-height: 1.25; }
.subnav .sub-link span { font-weight: 400; font-size: 12px; color: #6b7a88; }
.subnav .sub-link:hover { border-color: #0f6e62; }
.subnav .sub-link.active { background: #0f6e62; border-color: #0f6e62; color: #fff; }
.subnav .sub-link.active span { color: #d5ece8; }

/* 课标挂标：列表徽章 + 阅读区引用块 */
.lesson .std { display: inline-block; margin-left: 6px; padding: 0 5px; border-radius: 3px;
  font-size: 11px; line-height: 16px; color: #0b6b3a; background: #e6f4ec; border: 1px solid #bfe3cf; }
.stdbox { margin: 0 0 14px; padding: 10px 12px; border: 1px solid #e2e6ea; border-left: 3px solid #2f7d5d;
  background: #f7faf8; border-radius: 4px; }
.stdbox b { display: block; margin-bottom: 6px; font-size: 13px; color: #22543d; }
.stdbox .stline { margin: 0 0 8px; font-size: 13px; line-height: 1.7; color: #333; }
.stdbox .stline:last-child { margin-bottom: 0; }
.stdbox code { padding: 1px 4px; border-radius: 3px; background: #eef2f5; font-size: 12px; }
.stdbox .conf { font-size: 11px; color: #777; }