/* 资料实战局 · 设计系统
   清晰的训练工作台：纸面留白、墨色层级、朱红定位信号。 */
:root {
  --bg: #f6f7f4;
  --panel: #ffffff;
  --panel2: #eff1ec;
  --line: #dce2dc;
  --text: #202c29;
  --muted: #5d6b65;
  --green: #276b61;
  --yellow: #96622d;
  --red: #aa4437;
  --blue: #315b6a;
  --radius: 16px;
  --shadow: 0 12px 36px rgba(28, 52, 44, .045);
  --studio-ink: #20332f;
  --studio-bg: #f6f7f4;
  --studio-muted: #63716b;
  --studio-display: "Songti SC", "Noto Serif SC", "STSong", Georgia, serif;
  --studio-sans: -apple-system, BlinkMacSystemFont, "PingFang SC", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --studio-ink-soft: #31453f;
  --studio-accent: #aa4437;
  --studio-accent-wash: #f8ece8;
  --studio-surface: #fff;
  --studio-subtle: #eef1ed;
  --studio-rule: #dce2dc;
  --studio-ease: cubic-bezier(.23, 1, .32, 1);
}

html { scroll-padding-top: 24px; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  letter-spacing: -.012em;
}
body::selection, ::selection { background: #e3b8ae; color: var(--studio-ink); }
button, input, select, textarea { font-family: inherit; }
button { -webkit-tap-highlight-color: transparent; }
button:focus-visible, a:focus-visible, input:focus-visible, select:focus-visible {
  outline: 2px solid var(--studio-accent);
  outline-offset: 3px;
}
button:disabled { transform: none !important; box-shadow: none; }
@media (hover: hover) and (pointer: fine) {
  button:not(:disabled):hover { transition: color 160ms ease, background-color 160ms ease, border-color 160ms ease, box-shadow 160ms ease; }
}
button:not(:disabled):active { transform: scale(.985); transition: transform 120ms var(--studio-ease); }

/* 主框架 */
.shell { grid-template-columns: 248px minmax(0, 1fr); }
.side {
  z-index: 10;
  padding: 31px 18px 21px;
  color: var(--studio-ink);
  background: #eff2ee;
  border-right: 1px solid var(--studio-rule);
  box-shadow: none;
}
.brand {
  gap: 13px;
  margin: 0 10px 37px;
  align-items: center;
  color: var(--studio-ink);
  font-size: 19px;
  font-weight: 780;
  letter-spacing: -.035em;
  line-height: 1.25;
}
.brand small {
  display: block;
  margin-top: 4px;
  color: #7d8c83;
  font-size: 10px;
  font-weight: 620;
  letter-spacing: .14em;
}
.brand-mark {
  flex: 0 0 42px;
  width: 42px;
  height: 42px;
  border-radius: 12px;
  color: #fff;
  background: var(--studio-accent);
  box-shadow: 0 6px 15px rgba(170, 68, 55, .18);
  transform: none;
  font-family: "Songti SC", "Noto Serif SC", serif;
  font-size: 23px;
}
.nav { gap: 4px; }
.nav button {
  min-height: 48px;
  padding: 11px 13px;
  border: 1px solid transparent;
  border-radius: 10px;
  color: #5f7069;
  font-size: 14px;
  font-weight: 650;
  letter-spacing: .01em;
}
.nav svg { width: 18px; height: 18px; stroke-width: 1.8; }
.nav button.active {
  color: var(--studio-ink);
  background: #fff;
  border-color: #d9e0d9;
  box-shadow: 0 4px 14px rgba(27, 54, 44, .05);
}
.nav button.active::after {
  content: "";
  width: 5px;
  height: 5px;
  margin-left: auto;
  border-radius: 50%;
  background: var(--studio-accent);
}
@media (hover: hover) and (pointer: fine) {
  .nav button:hover { color: var(--studio-ink); background: #fff; }
}
.side-foot {
  padding: 17px;
  border: 1px solid #d8dfd8;
  border-radius: 12px;
  background: #f9faf7;
}
.rank { color: #78867e; font-size: 12px; }
.rank strong { color: var(--studio-ink); font-size: 15px; letter-spacing: -.01em; }
.bar { height: 5px; background: #e0e6df; }
.bar i { background: var(--studio-accent); }
.shell > main { max-width: 1550px; padding: 40px clamp(24px, 3.3vw, 58px) 72px; }

/* 今日训练：把下一步与材料放在首屏 */
.top { align-items: end; gap: 20px; margin-bottom: 30px; }
.eyebrow {
  color: var(--studio-accent);
  font-size: 11px;
  font-weight: 780;
  letter-spacing: .17em;
}
.top h1 {
  margin-top: 10px;
  color: var(--studio-ink);
  font-family: "Songti SC", "Noto Serif SC", serif;
  font-size: clamp(29px, 3.1vw, 43px);
  font-weight: 750;
  letter-spacing: -.06em;
  line-height: 1.2;
}
.profile { gap: 13px; }
.streak {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  padding: 8px 0;
  color: #697b70;
  background: none;
  border: 0;
  font-size: 13px;
}
.streak::before {
  content: "";
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--studio-accent);
}
.avatar {
  width: 40px;
  height: 40px;
  color: #fff;
  background: var(--studio-ink);
  border-radius: 12px;
  box-shadow: none;
  font-size: 13px;
}
.summary { grid-template-columns: minmax(0, 1.55fr) minmax(270px, .7fr); gap: 16px; margin-bottom: 17px; }
.mission, .quick, .card { box-shadow: var(--shadow); }
.mission {
  min-height: 254px;
  padding: 28px 30px 22px;
  border: 1px solid var(--studio-rule);
  border-radius: var(--radius);
  background:
    linear-gradient(90deg, transparent calc(100% - 1px), rgba(55, 85, 71, .04) calc(100% - 1px)),
    linear-gradient(0deg, transparent calc(100% - 1px), rgba(55, 85, 71, .04) calc(100% - 1px)),
    #fff;
  background-size: 22px 22px;
}
.mission::after { display: none; }
.mission-row { align-items: flex-start; }
.mission h2 {
  margin: 11px 0 10px;
  max-width: 680px;
  color: var(--studio-ink);
  font-family: "Songti SC", "Noto Serif SC", serif;
  font-size: clamp(22px, 2.1vw, 30px);
  font-weight: 740;
  letter-spacing: -.045em;
  line-height: 1.35;
}
.mission p { max-width: 600px; color: #5c6b63; font-size: 14px; line-height: 1.7; }
.mission-actions { gap: 8px; margin-top: 22px; }
.start-set {
  min-height: 42px;
  padding: 10px 15px;
  border-radius: 9px;
  color: #fff;
  background: var(--studio-ink);
  box-shadow: none;
  font-size: 13px;
  font-weight: 700;
}
.start-set.secondary {
  color: var(--studio-ink);
  background: #f5f7f4;
  box-shadow: inset 0 0 0 1px #d6ded6;
}
@media (hover: hover) and (pointer: fine) {
  .start-set:hover { background: #314c45; }
  .start-set.secondary:hover { background: #edf1ec; }
}
.goal-ring {
  flex: 0 0 76px;
  width: 76px;
  height: 76px;
  margin: 0;
  border: 1px solid #d9e1da;
  border-radius: 13px;
  color: var(--studio-accent);
  background: #f8f9f6;
}
.goal-ring::before { display: none; }
.goal-ring span { font: 760 19px/1 -apple-system, BlinkMacSystemFont, "PingFang SC", sans-serif; letter-spacing: -.05em; }
.steps {
  margin-top: 26px;
  padding-top: 17px;
  border-top: 1px solid var(--studio-rule);
}
.step-dot { color: #8a9a91; font-size: 11px; font-weight: 650; white-space: nowrap; }
.step-dot::before { width: 6px; height: 6px; background: #bec9be; }
.step-dot::after { background: #dce3dc; }
.step-dot.done::before { background: var(--green); }
.step-dot.current::before { background: var(--studio-accent); box-shadow: 0 0 0 4px #f4ddd8; }
.quick {
  display: flex;
  flex-direction: column;
  min-height: 254px;
  padding: 27px;
  border: 1px solid var(--studio-ink);
  border-radius: var(--radius);
  color: #f6f9f5;
  background: var(--studio-ink);
}
.quick h3 { color: #f6f9f5; font-size: 15px; }
.quick .delta { color: #b8d7c4; font-size: 12px; }
.quick .metrics { margin-top: 24px; gap: 9px; }
.quick .metric {
  min-height: 85px;
  padding: 13px 14px;
  border: 1px solid rgba(235, 247, 239, .13);
  border-radius: 10px;
  color: #f6f9f5;
  background: rgba(255, 255, 255, .055);
}
.quick .metric span, .quick .weak { color: #b9c9bf; }
.quick .metric b { font-size: 25px; letter-spacing: -.05em; font-variant-numeric: tabular-nums; }
.quick .weak { margin-top: auto; padding-top: 15px; border-color: rgba(235, 247, 239, .16); }
.quick .weak strong { color: #f4c4b7; }

.workbench { grid-template-columns: minmax(0, 1.18fr) minmax(340px, .82fr); gap: 16px; align-items: stretch; }
.card { border: 1px solid var(--studio-rule); border-radius: var(--radius); background: #fff; }
.material { padding: clamp(22px, 2.3vw, 32px); }
.card-title { gap: 12px; margin-bottom: 20px; }
.card-title h3 { color: var(--studio-ink); font-size: 16px; font-weight: 740; }
.tag {
  padding: 7px 9px;
  border: 1px solid #e8d0c9;
  border-radius: 6px;
  color: var(--studio-accent);
  background: #fbf2ef;
  font-size: 11px;
  font-weight: 700;
}
.question {
  padding: 16px 19px;
  margin-bottom: 22px;
  border-left: 3px solid var(--studio-accent);
  border-radius: 0 9px 9px 0;
  color: var(--studio-ink);
  background: #f6f7f4;
  font-size: 18px;
  font-weight: 700;
  line-height: 1.65;
}
.source { color: #34433d; font-size: 15px; line-height: 2.02; }
.source p { margin-bottom: 13px; }
.source button { color: #974137; text-decoration-color: #c99287; text-decoration-thickness: 1px; }
.source button.selected { color: #165f56; background: #e1f0e9; }
.hint { margin-top: 24px; padding-top: 17px; color: #6a7c70; font-size: 12px; }
.task { padding: clamp(22px, 2.3vw, 32px); background: #fbfcf9; }
.counter { color: var(--studio-accent); font-size: 11px; font-weight: 760; }
.timer {
  padding: 8px 10px;
  border: 1px solid #e4ded6;
  border-radius: 8px;
  color: var(--studio-ink);
  background: #fff;
  font-size: 13px;
}
.task h2 { margin-top: 11px; color: var(--studio-ink); font-size: 22px; letter-spacing: -.035em; }
.task > p { color: #66766d; font-size: 14px; line-height: 1.65; }
.pick-list { gap: 8px; }
.pick {
  padding: 13px 15px;
  border: 1px solid #dce4dc;
  border-radius: 9px;
  color: var(--studio-ink);
  background: #fff;
  line-height: 1.5;
  transition: border-color 160ms ease, background-color 160ms ease, transform 120ms var(--studio-ease);
}
@media (hover: hover) and (pointer: fine) {
  .pick:hover { border-color: #9ebaae; transform: none; background: #f7faf7; }
}
.pick.selected { border-color: #27766b; color: #20594f; background: #eaf4ee; }
.primary, .ghost { min-height: 43px; padding: 11px 16px; border-radius: 9px; font-size: 14px; }
.primary { color: #fff; background: var(--studio-accent); box-shadow: none; }
.ghost { color: var(--studio-ink); background: #e9eee8; }
.feedback.show { border: 1px solid transparent; }
.feedback.ok { color: #205e50; background: #e7f3eb; border-color: #c9e2d4; }
.feedback.bad { color: #963c36; background: #fbefec; border-color: #edd3cc; }
.diagnostic { border-top: 3px solid var(--studio-accent); }
.diagnostic.show { animation: none; }
.diagnosis { background: #f6f8f4; border-color: #dfe6de; }
.pulse { background: var(--studio-accent); }

@media (max-width: 1150px) {
  .shell { grid-template-columns: 210px minmax(0, 1fr); }
  .side { padding: 25px 13px 17px; }
  .brand { margin: 0 8px 28px; font-size: 17px; }
  .summary, .workbench { grid-template-columns: 1fr; }
  .quick { min-height: auto; }
  .quick .metrics { margin-top: 16px; }
  .quick .weak { margin-top: 17px; }
  .task { min-height: 330px; }
}
@media (max-width: 720px) {
  .shell { display: block; }
  .side {
    display: block;
    position: sticky;
    top: 0;
    height: auto;
    padding: 9px 11px 10px;
    overflow: hidden;
    border-right: 0;
    border-bottom: 1px solid var(--studio-rule);
    background: rgba(246, 248, 244, .96);
    backdrop-filter: blur(16px);
  }
  .brand, .side-foot, .mobile-nav { display: none; }
  .nav { display: flex; gap: 5px; overflow-x: auto; scrollbar-width: none; }
  .nav::-webkit-scrollbar { display: none; }
  .nav button { flex: 0 0 auto; min-height: 38px; padding: 8px 11px; white-space: nowrap; font-size: 12px; }
  .nav button svg, .nav button.active::after { display: none; }
  .shell > main { padding: 25px 16px 50px; }
  .top { margin-bottom: 21px; }
  .top h1 { font-size: clamp(27px, 7vw, 35px); }
  .profile .streak { display: none; }
  .avatar { width: 34px; height: 34px; }
  .mission, .quick, .material, .task { padding: 20px; }
  .mission { min-height: 0; }
  .mission-row { display: block; }
  .goal-ring { display: none; }
  .mission-actions { padding-right: 0; }
  .steps { overflow-x: auto; margin-top: 24px; }
  .step-dot { min-width: 67px; }
  .summary, .workbench { gap: 12px; }
  .quick .metrics { grid-template-columns: 1fr 1fr; }
  .card-title { align-items: start; }
  .tag { text-align: center; }
  .question { font-size: 17px; }
  .task { min-height: 0; }
}
@media (max-width: 420px) {
  .top h1 { font-size: 28px; line-height: 1.2; }
  .top h1 span { display: block; }
  .top .avatar { display: none; }
  .mission-actions { display: grid; }
  .start-set { width: 100%; }
  .quick .metrics { grid-template-columns: 1fr 1fr; }
  .card-title { display: block; }
  .tag { display: inline-block; margin-top: 10px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  button:not(:disabled):active { transform: none; }
  .pick { transition: border-color 160ms ease, background-color 160ms ease; }
}

/* The study surfaces share one quiet editorial system. */
.exam-overlay, .stem-overlay, .basic-overlay, .course-overlay, .module-book-overlay {
  background: var(--studio-bg);
  color: var(--studio-ink);
}
.exam-head, .module-book-head, .course-homework-head {
  min-height: 76px;
  height: auto;
  padding: 16px clamp(20px, 3vw, 48px);
  background: #fff;
  border-bottom: 1px solid var(--studio-rule);
  box-shadow: none;
}
.exam-head h2, .module-book-head h2 {
  font-family: var(--studio-display);
  font-size: clamp(19px, 1.8vw, 26px);
  font-weight: 650;
  letter-spacing: -.035em;
  line-height: 1.3;
}
.exam-meta { color: var(--studio-muted); gap: 20px; }
.close-exam, .course-homework-back {
  border: 1px solid var(--studio-rule);
  border-radius: 8px;
  background: #fff;
  color: var(--studio-ink);
  font: 650 13px var(--studio-sans);
  padding: 9px 14px;
  cursor: pointer;
  white-space: nowrap;
  transition: background-color 160ms ease, border-color 160ms ease;
}
@media (hover: hover) and (pointer: fine) {
  .close-exam:hover, .course-homework-back:hover { background: #f1f5ef; border-color: #a4b5aa; }
}
.exam-overlay main, .stem-overlay main, .basic-overlay main, .course-overlay main, .module-book-overlay main {
  max-width: none;
  margin: 0;
}

/* Course: index at left, spacious reading desk at right. */
.course-layout { grid-template-columns: minmax(248px, 292px) minmax(0, 1fr); min-height: 0; }
.course-menu {
  padding: 22px 13px 28px;
  background: #f0f3ee;
  border-right: 1px solid var(--studio-rule);
  overflow-y: auto;
  scrollbar-width: thin;
}
.course-progress { margin: 0 10px 21px; padding: 17px; border: 1px solid var(--studio-rule); border-radius: 10px; background: #fff; }
.course-progress-head { color: var(--studio-muted); font-size: 12px; }
.course-progress-head b { color: var(--studio-ink); font-variant-numeric: tabular-nums; }
.course-progress .bar { margin-top: 10px; background: #e6ebe4; }
.course-progress .bar i { background: var(--studio-accent); }
.course-list { gap: 2px; }
.course-chapter { color: var(--studio-muted); font-size: 11px; letter-spacing: .13em; padding: 20px 17px 7px; }
.course-list button { border-radius: 8px; color: #53615a; min-height: 43px; font-family: var(--studio-sans); font-size: 13px; }
.course-list button.active { background: #fff; color: #1c594c; box-shadow: inset 3px 0 var(--studio-accent); }
@media (hover: hover) and (pointer: fine) { .course-list button:hover { background: #fff; color: var(--studio-ink); } }
.course-content { overflow-y: auto; padding: clamp(26px, 3.4vw, 54px) clamp(22px, 5vw, 84px) 90px; background: var(--studio-bg); }
.course-lesson { max-width: 950px; margin: 0 auto; }
.course-kicker, .lesson-unit-index { color: var(--studio-accent); font-size: 11px; font-weight: 750; letter-spacing: .13em; }
.course-lesson h1 { font-family: var(--studio-display); font-size: clamp(36px, 4vw, 56px); letter-spacing: -.055em; line-height: 1.15; margin: 12px 0 18px; }
.course-lead { max-width: 70ch; color: var(--studio-muted); font-size: 17px; line-height: 1.9; }
.lesson-outline { gap: 10px; margin: 28px 0 40px; }
.lesson-outline-item { min-height: 112px; border: 1px solid var(--studio-rule); border-radius: 11px; background: #fff; box-shadow: none; transition: border-color 160ms ease, background-color 160ms ease, transform 160ms var(--studio-ease); }
.lesson-outline-item:hover { border-color: #9cb4a5; background: #f9fbf8; }
.lesson-outline-item.active { border-color: #78a48c; background: #eff6f0; box-shadow: inset 0 0 0 1px #78a48c; }
.lesson-outline-item b { color: var(--studio-ink); }
.lesson-outline-item span { color: var(--studio-muted); }
.lesson-unit { margin: 32px 0; padding: clamp(23px, 3vw, 37px); border: 1px solid var(--studio-rule); border-radius: 13px; background: #fff; box-shadow: 0 8px 30px rgba(18, 44, 37, .025); }
.lesson-unit-head { border-bottom-color: var(--studio-rule); }
.lesson-unit h3, .lesson-unit-head h3 { color: var(--studio-ink); font-family: var(--studio-display); font-size: clamp(23px, 2.3vw, 30px); letter-spacing: -.025em; }
.lesson-unit p, .course-lesson p { line-height: 1.8; }
.course-concept, .course-formula, .course-tip, .lesson-scenario, .lesson-story, .lesson-bridge, .lesson-example, .course-quiz,
.quantity-card, .formula-row, .lesson-concept-visual, .module-example, .method-limit, .module-purpose, .correction-formula, .error-budget {
  border-color: var(--studio-rule); border-radius: 10px; box-shadow: none;
}
.course-concept, .lesson-scenario, .lesson-story, .lesson-bridge, .module-example, .quantity-card { background: #f8faf6; }
.course-formula, .formula-row, .module-purpose, .correction-formula, .error-budget { background: #eff5ef; color: #244b3d; }
.course-tip, .method-limit { background: #fbf5ec; }
.course-quiz { background: #f8faf6; }
.course-answers button, .course-answer, .lesson-check-answer { background: #fff; color: var(--studio-ink); border-color: var(--studio-rule); border-radius: 8px; }
.course-answers button.selected, .course-answer.selected, .lesson-check-answer.selected { background: #eaf4ee; border-color: #73a48a; color: #205a47; }
.course-next, .course-complete, .course-actions button { border-radius: 8px; }
.lesson-concept-visual { max-width: 100%; background: #f6f8f3; overflow: hidden; }
.lesson-concept-visual img { background: #f6f8f3; }
.lesson-concept-visual figcaption { border-top: 1px solid var(--studio-rule); color: var(--studio-muted); font-family: var(--studio-sans); font-size: 12px; }

/* Homework keeps the lesson context while making the exercise the focal point. */
.course-homework { background: var(--studio-bg); }
.course-homework-head { position: sticky; top: 0; z-index: 2; }
.course-homework-brand { color: var(--studio-ink); font-family: var(--studio-display); letter-spacing: -.02em; }
.course-homework-brand small { color: var(--studio-muted); font-family: var(--studio-sans); letter-spacing: 0; }
.course-homework-shell { max-width: 1470px; margin: 0 auto; padding: clamp(24px, 3vw, 48px) clamp(17px, 3vw, 45px) 80px; }
.course-homework-intro { margin-bottom: 27px; }
.course-homework-intro h1 { color: var(--studio-ink); font-family: var(--studio-display); font-size: clamp(31px, 3.4vw, 48px); letter-spacing: -.05em; margin: 8px 0 12px; }
.course-homework-intro p { color: var(--studio-muted); font-size: 14px; line-height: 1.7; }
.course-homework-layout { grid-template-columns: minmax(0, 1fr) minmax(220px, 264px); gap: 24px; align-items: start; }
.course-homework-layout > main { padding: 0; min-width: 0; }
.course-homework-question, .course-homework-result, .course-homework-side { border: 1px solid var(--studio-rule); border-radius: 12px; background: #fff; box-shadow: none; }
.course-homework-question { padding: clamp(22px, 3vw, 37px); }
.course-homework-side { top: 24px; padding: 21px; }
.course-homework-side h3 { font-family: var(--studio-display); color: var(--studio-ink); }
.course-homework-side p { color: var(--studio-muted); }
.course-homework-grid button { border-radius: 6px; background: #f7f9f6; border-color: var(--studio-rule); }
.course-homework-grid button.current { border-color: var(--studio-accent); color: var(--studio-accent); }
.course-homework-grid button.done { background: #e9f2e9; border-color: #a4c5ad; color: #28604b; }
.course-homework-primary, .course-homework-secondary { border-radius: 8px; }
.course-homework-primary { background: var(--studio-accent); color: #fff; }
.course-homework-secondary { color: var(--studio-ink); background: #eaf0e9; }
.course-homework-material, .course-homework-explanation { background: #f7faf6; border-color: var(--studio-rule); }
.course-homework-option { border-color: var(--studio-rule); background: #fff; border-radius: 8px; }
.course-homework-option.selected { border-color: #70a18a; background: #eaf4ee; }
.course-homework-lesson-link { border-color: #b8d5bc; background: #f0f7ef; }

/* Practice index and timed workspaces. */
.basic-page { overflow-y: auto; background: var(--studio-bg); padding: 0; }
.basic-inner { max-width: 1370px; padding: clamp(28px, 3.3vw, 48px) clamp(18px, 4vw, 58px) 80px; }
.basic-intro { margin-bottom: 32px; }
.basic-intro h2 { font: 650 clamp(32px, 3.4vw, 46px)/1.2 var(--studio-display); letter-spacing: -.045em; color: var(--studio-ink); }
.basic-intro p { max-width: 62ch; color: var(--studio-muted); font-size: 15px; line-height: 1.8; }
.basic-count { background: #edf3ec; color: #3a6854; border: 1px solid #d7e6da; border-radius: 6px; }
.basic-grid { gap: 14px; }
.basic-module { border-color: var(--studio-rule); border-radius: 12px; background: #fff; box-shadow: none; padding: 27px; }
.basic-index { color: #fff; background: var(--studio-accent); font: 700 12px var(--studio-sans); letter-spacing: .12em; }
.basic-module h3 { color: var(--studio-ink); font: 650 26px var(--studio-display); letter-spacing: -.03em; }
.basic-module p { color: var(--studio-muted); line-height: 1.75; }
.basic-module footer { border-top-color: var(--studio-rule); }
.basic-enter { background: var(--studio-accent); color: #fff; border-radius: 7px; }
.stem-body { background: var(--studio-bg); padding: clamp(16px, 2.6vw, 36px); }
.stem-wrap { max-width: 1560px; gap: 18px; grid-template-columns: minmax(450px, 1.1fr) minmax(400px, .9fr); }
.stem-card { background: #fff; border-color: var(--studio-rule); border-radius: 11px; box-shadow: none; padding: clamp(20px, 2.4vw, 32px); }
.stem-number, .question-kicker { color: var(--studio-accent); }
.stem-material { color: var(--studio-ink); }
.stem-text { font-family: var(--studio-display); font-weight: 650; }
.stem-material th, .material-copy th { background: #eaf1e9; }
.stem-material th, .stem-material td, .material-copy th, .material-copy td { border-color: #d2ddd2; }
.stem-original-options li, .identify-row, .choice-chip, .formula-choice, .eliminate-option, .speed-strategy { border-color: var(--studio-rule); background: #fff; color: var(--studio-ink); }
.identify-row { border-radius: 9px; }
.choice-chip { border-radius: 7px; transition: background-color 160ms ease, border-color 160ms ease; }
.choice-chip.selected, .formula-choice.selected, .eliminate-option.selected, .speed-strategy.selected { border-color: #74a58b; background: #eaf4ee; box-shadow: inset 0 0 0 1px #74a58b; color: #205a47; }
.stem-submit, .timer-toggle, .stem-nav .next-question { background: var(--studio-accent); color: #fff; border-radius: 7px; }
.stem-nav button { background: #eaf0e9; color: var(--studio-ink); }
.stem-result, .time-box, .time-box.total { background: #f4f8f3; border-color: var(--studio-rule); }
.time-box strong, .time-box.total strong { color: var(--studio-accent); }
.stem-dot, .answer-dot { background: #fff; border-color: var(--studio-rule); }
.stem-dot.current, .answer-dot.current { box-shadow: inset 0 0 0 2px var(--studio-accent); color: var(--studio-accent); }
.capture-num { color: #235e50; background: #e8f1ea; }
.capture-num.selected { background: var(--studio-accent); color: #fff; }

/* Exam has two equally useful reading and answer surfaces. */
.exam-body { grid-template-columns: minmax(0, 1.15fr) minmax(390px, .85fr); }
.paper-pane { background: #edf2ec; border-right: 1px solid var(--studio-rule); padding: 20px; }
.paper-frame { background: #fff; border: 1px solid var(--studio-rule); border-radius: 10px; box-shadow: none; }
.material-copy { color: var(--studio-ink); }
.paper-actions button { background: #fff; border-color: var(--studio-rule); color: var(--studio-ink); }
.answer-pane { background: #fff; padding: clamp(22px, 3vw, 45px); }
.exam-question { font-family: var(--studio-display); font-weight: 580; line-height: 1.7; }
.exam-option { border-color: var(--studio-rule); background: #fff; color: var(--studio-ink); border-radius: 8px; }
.exam-option.selected { border-color: #6fa087; background: #eaf4ee; box-shadow: inset 3px 0 var(--studio-accent); }
.exam-next, .submit-set { background: var(--studio-accent); color: #fff; }
.exam-prev { background: #eaf0e9; color: var(--studio-ink); }
.answer-sheet { border-top-color: var(--studio-rule); }

/* Narrow screens retain every route and a readable single-column task. */
.module-book-overlay { grid-template-rows:auto minmax(0,1fr); }
.module-book-layout { grid-template-columns: 255px minmax(0,1fr); background: var(--studio-bg); }
.module-book-menu { top: 0; height: 100%; max-height: calc(100vh - 76px); padding: 24px 12px; background: #f0f3ee; border-right: 1px solid var(--studio-rule); }
.module-book-menu-intro { padding: 3px 12px 18px; }
.module-book-menu-intro strong { color: var(--studio-ink); font: 650 17px var(--studio-display); }
.module-book-menu-intro span { color: var(--studio-muted); }
.module-book-list button { border-radius: 7px; color: #53615a; font-family: var(--studio-sans); }
.module-book-list button.active { border-color: var(--studio-rule); background: #fff; color: #205d4e; box-shadow: inset 3px 0 var(--studio-accent); }
@media (hover: hover) and (pointer: fine) { .module-book-list button:hover { background: #fff; } }
.module-book-list button small { color: var(--studio-muted); }
.module-book-main { padding: clamp(22px, 3vw, 42px) clamp(18px, 4vw, 62px) 80px; }
.module-book-top { max-width: 1120px; margin: 0 auto 23px; }
.module-book-top h2 { color: var(--studio-ink); font: 650 clamp(28px, 3vw, 43px)/1.2 var(--studio-display); letter-spacing: -.045em; }
.module-book-top p { color: var(--studio-muted); font-size: 14px; }
.module-book-score { color: var(--studio-accent); font-variant-numeric: tabular-nums; white-space: nowrap; }
.module-book-question { border-color: var(--studio-rule); border-radius: 12px; background: #fff; box-shadow: none; }
.module-book-panel-head { min-height: 75px; padding: 16px clamp(20px, 3vw, 36px); border-color: var(--studio-rule); }
.module-book-panel-head strong { font: 650 20px var(--studio-display); }
.module-book-panel-head small { color: var(--studio-muted); font-family: var(--studio-sans); }
.module-book-question-scroll { padding: clamp(21px, 3vw, 38px); }
.module-book-stem { color: var(--studio-ink); font: 580 clamp(18px, 1.8vw, 22px)/1.75 var(--studio-display); }
.module-book-options button { border-color: var(--studio-rule); background: #fff; color: var(--studio-ink); border-radius: 8px; font: 550 16px/1.55 var(--studio-sans); padding: 15px 18px; transition: background-color 160ms ease, border-color 160ms ease; }
.module-book-options button.selected { border-color: #72a48a; background: #eaf4ee; box-shadow: inset 3px 0 var(--studio-accent); }
.module-book-options button.correct { border-color: #71a88a; background: #e8f5e9; }
.module-book-options button.wrong { border-color: #c47d72; background: #fceeea; }
.module-book-feedback { color: var(--studio-muted); }
.module-book-nav button { background: #eaf0e9; color: var(--studio-ink); }
.module-book-nav button:last-child, .module-book-submit { background: var(--studio-accent); color: #fff; }
.module-book-sheet button { background: #fff; border-color: var(--studio-rule); color: var(--studio-muted); }
.module-book-sheet button.answered { background: #e9f2e9; border-color: #b9d5bd; color: #276149; }
.module-book-sheet button.current { outline-color: var(--studio-accent); }
.module-book-native-content { color: var(--studio-ink); }
.module-book-native-source { border-top-color: var(--studio-rule); color: var(--studio-muted); }
.module-book-native-table-wrap, .module-book-native-chart, .module-book-svg-chart { background: #fff; border-color: var(--studio-rule); }
.module-book-native-table td, .module-book-native-table th { border-color: #d8e1d7; }
.module-book-native-table tr:first-child td, .module-book-native-table th { background: #eaf1e9; }
.module-book-native-table tr:nth-child(even) { background: #f8faf7; }
.module-book-chart-legend { color: var(--studio-muted); }
.module-book-svg-chart .chart-label { fill: var(--studio-ink); }
@media (max-width: 1000px) {
  .module-book-layout { grid-template-columns: 210px minmax(0,1fr); }
  .module-book-main { padding: 23px; }
}
@media (max-width: 1100px) {
  .course-layout { grid-template-columns: 235px minmax(0, 1fr); }
  .lesson-outline { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .course-homework-layout { grid-template-columns: minmax(0, 1fr) 220px; }
}
@media (max-width: 800px) {
  .course-layout { display: block; overflow-y: auto; }
  .course-menu { position: relative; max-height: 250px; border-right: 0; border-bottom: 1px solid var(--studio-rule); }
  .course-content { overflow: visible; padding: 26px 18px 60px; }
  .course-homework-layout { display: flex; flex-direction: column; }
  .course-homework-layout > main, .course-homework-side { width: 100%; }
  .course-homework-side { position: static; order: -1; }
  .stem-wrap, .exam-body { display: block; }
  .stem-card.sticky { position: static; }
  .stem-reading { max-height: none; }
  .paper-pane { min-height: 280px; max-height: 50vh; }
  .answer-pane { min-height: 50vh; }
}
@media (max-width: 600px) {
  .exam-head, .module-book-head, .course-homework-head { padding: 12px 16px; min-height: 65px; gap: 8px; }
  .exam-head h2, .module-book-head h2 { font-size: 17px; }
  .exam-meta > span { display: none; }
  .close-exam, .course-homework-back { padding: 8px 10px; font-size: 11px; }
  .course-lesson h1 { font-size: 33px; }
  .lesson-outline { grid-template-columns: 1fr 1fr; gap: 7px; }
  .lesson-outline-item { min-height: 100px; }
  .lesson-unit { padding: 20px; }
  .stem-body { padding: 11px; }
  .stem-card { padding: 19px; margin-bottom: 11px; }
  .stem-original-options { grid-template-columns: 1fr; }
  .course-homework-shell { padding: 22px 12px 60px; }
  .course-homework-question { padding: 19px; }
  .basic-module { padding: 22px; }
  .module-book-layout { display: block; overflow-y: auto; }
  .module-book-menu { position: static; height: auto; max-height: 110px; padding: 7px; overflow-x: auto; border-right: 0; border-bottom: 1px solid var(--studio-rule); }
  .module-book-main { padding: 18px 12px 60px; }
  .module-book-top { align-items: flex-start; }
  .module-book-top h2 { font-size: 26px; }
  .module-book-question-scroll { padding: 18px; }
  .module-book-options button { font-size: 14px; }
  .module-book-stem { font-size: 18px; }
}