.unit-card { display: flex; flex-direction: column; padding: 24px; cursor: pointer; transition: border-color .18s; position: relative; overflow: hidden; }
.unit-card:hover { border-color: var(--border-2); }
.unit-card:focus-visible, .lesson-item:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-color: var(--accent); }
.unit-card .uic { font-family: var(--font); font-size: 13px; color: var(--text-dim); margin-bottom: 16px; padding-right: 80px; }
.unit-card h3 { font-size: 19px; line-height: 1.35; margin-bottom: 10px; }
.unit-card p { flex: 1; font-size: 15px; color: var(--text-dim); margin-bottom: 24px; line-height: 1.65; }
.unit-card .progress { margin-bottom: 9px; }
.unit-card .meta { display: flex; justify-content: space-between; gap: 12px; font-size: 13px; color: var(--text-dim); font-family: var(--font); }
.unit-card .ucomplete { position: absolute; top: 24px; right: 24px; font-size: 12px; color: var(--accent); font-family: var(--font); }

.lesson-item { display: flex; align-items: center; gap: 14px; padding: 14px 18px; border: 1px solid var(--border); border-radius: var(--radius); margin-bottom: 8px; background: var(--bg); cursor: pointer; transition: all .2s; }
.lesson-item:hover { border-color: var(--border-2); transform: translateX(4px); }
.lesson-num { width: 34px; height: 34px; border-radius: 8px; display: grid; place-items: center; font-family: var(--mono); font-weight: 500; background: var(--bg-2); border: 1px solid var(--border); font-size: 13px; flex-shrink: 0; color: var(--text-dim); }
.lesson-item.done .lesson-num { background: var(--accent); color: var(--accent-ink); border-color: transparent; }
.lesson-item .li-info { flex: 1; }
.lesson-item .li-info h4 { font-size: 15px; margin-bottom: 3px; }
.lesson-item .li-info p { font-size: 12px; color: var(--text-faint); }
.lesson-item .li-check { color: var(--accent); font-size: 11px; letter-spacing: 0.1em; text-transform: uppercase; }

.lesson-main { max-width: 820px; margin: 0 auto; }
.lesson-content, .lesson-quiz { padding: clamp(20px, 4vw, 40px); }
.lesson-content { font-size: 17px; line-height: 1.85; }
.lesson-content h2 { font-size: clamp(26px, 3vw, 34px); line-height: 1.25; margin-bottom: 24px; }
.lesson-content h3 { margin: 32px 0 12px; color: var(--accent); }
.lesson-content h4 { font-size: 17px; margin: 24px 0 10px; }
.lesson-content > p { margin: 16px 0; }
.lesson-content ul { padding-left: 22px; margin: 16px 0; }
.lesson-content ol { padding-left: 24px; margin: 16px 0; }
.lesson-content li { margin-bottom: 8px; }
.lesson-content > :last-child { margin-bottom: 0; }
.lesson-content .lesson-stub-note { background: var(--surface-2); border-left: 3px solid var(--accent-2); padding: 12px 16px; border-radius: var(--radius); color: var(--text-dim); }
.lesson-quiz h4 { font-size: 21px; margin-bottom: 24px; }

.quiz-q { font-size: 17px; line-height: 1.6; font-weight: 600; margin-bottom: 16px; }
.quiz-opt { display: block; width: 100%; min-height: 48px; padding: 14px 16px; border: 1px solid var(--border-2); border-radius: var(--radius); margin-bottom: 10px; cursor: pointer; transition: border-color .2s, background .2s; font-size: 16px; font-family: var(--font); line-height: 1.55; text-align: left; color: var(--text); background: var(--bg-2); }
.quiz-opt:hover { border-color: var(--accent); }
.quiz-opt:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.quiz-opt:disabled { cursor: default; opacity: 1; }
.quiz-opt.correct { border-color: var(--bull); background: rgba(0,229,168,0.1); }
.quiz-opt.wrong { border-color: var(--bear); background: rgba(255,93,115,0.1); }
.quiz-explain { font-size: 15px; line-height: 1.7; color: var(--text-dim); margin-top: 12px; }
.quiz-block { padding-bottom: 28px; margin-bottom: 28px; border-bottom: 1px solid var(--rule); }
.quiz-block:last-child { padding-bottom: 0; margin-bottom: 0; border-bottom: none; }

/* responsive 16:9 YouTube embed */
.lesson-content .lesson-video { position: relative; width: 100%; aspect-ratio: 16 / 9; margin: 18px 0; border-radius: var(--radius); overflow: hidden; border: 1px solid var(--border); background: #000; }
.lesson-content .lesson-video iframe { position: absolute; inset: 0; width: 100%; height: 100%; border: 0; }

.lesson-content .lesson-video-block { margin: 22px 0; padding: 16px; border: 1px solid var(--border); border-radius: var(--radius); background: rgba(255,255,255,0.025); }
.lesson-content .lesson-video-block h4 { margin: 0 0 4px; font-size: 15px; }
.lesson-content .lesson-video-block .lesson-video-note { margin: 0; color: var(--text-dim); font-size: 13.5px; line-height: 1.55; }
.lesson-content .lesson-video-block .lesson-video { margin: 12px 0 0; }

/* figure + caption */
.lesson-content .lesson-figure { margin: 18px 0; }
.lesson-content .lesson-figure img { width: 100%; border-radius: var(--radius); border: 1px solid var(--border); display: block; }
.lesson-content .lesson-figure figcaption { font-size: 12.5px; color: var(--text-faint); margin-top: 8px; text-align: center; }

/* callout / quote */
.lesson-content .lesson-quote { margin: 18px 0; padding: 14px 18px; border-left: 3px solid var(--accent); background: rgba(121,201,145,0.07); border-radius: 0 10px 10px 0; color: var(--text); font-style: italic; }

/* Formula box: sets equations apart from paragraph text */
.lesson-content .lesson-formula {
  margin: 22px 0;
  padding: 16px 20px;
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent-2);
  border-radius: var(--radius);
  background: var(--surface-2);
}
.lesson-content .lesson-formula .lesson-block-label { color: var(--accent-2); margin-bottom: 12px; }
.lesson-content .lesson-formula-expr {
  font-family: var(--mono);
  font-size: 18px;
  line-height: 1.7;
  color: var(--text);
  text-align: center;
  padding: 6px 4px;
  overflow-x: auto;
  overflow-y: hidden;
}
/* KaTeX-typeset formulas: reset the display wrapper and size the math up a touch */
.lesson-content .lesson-formula-expr .katex-display { margin: 0; padding: 4px 0; }
.lesson-content .lesson-formula-expr .katex { font-size: 1.2em; color: var(--text); }
.lesson-content .lesson-formula-where {
  list-style: none;
  margin: 14px 0 0;
  padding: 12px 0 0;
  border-top: 1px solid var(--rule);
  display: flex;
  flex-wrap: wrap;
  gap: 7px 22px;
  font-size: 13px;
}
.lesson-content .lesson-formula-where li { color: var(--text-dim); font-family: var(--mono); }
.lesson-content .lesson-formula-caption { margin: 10px 0 0; font-size: 14px; color: var(--text-faint); text-align: center; }

/* Structured teaching blocks */
.lesson-objectives, .lesson-terms, .lesson-example, .lesson-activity {
  margin: 24px 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  background: rgba(255,255,255,0.025);
}

.lesson-objectives { border-left: 3px solid var(--accent); background: rgba(121,201,145,0.065); }
.lesson-content .lesson-objectives h3,
.lesson-content .lesson-terms h3,
.lesson-content .lesson-example h3,
.lesson-content .lesson-activity h3 { margin: 0 0 10px; color: var(--text); font-size: 21px; }
.lesson-objectives ul { margin-bottom: 0; }
.lesson-objectives li::marker { color: var(--accent); }

.lesson-terms dl { display: grid; gap: 0; }
.lesson-term { display: grid; grid-template-columns: minmax(130px, .55fr) 1.45fr; gap: 18px; padding: 12px 0; border-top: 1px solid var(--rule); }
.lesson-term:first-child { border-top: 0; padding-top: 2px; }
.lesson-term:last-child { padding-bottom: 0; }
.lesson-term dt { color: var(--text); font-weight: 650; }
.lesson-term dd { color: var(--text-dim); }

.lesson-example { border-color: var(--border-2); background: var(--surface-2); }
/* Kicker labels ("Worked example", "Calculation", "Formula", etc.) are hidden:
   they read as templated. This is display-only; the lesson content and activities
   are unchanged, so no re-seed and no user data is touched. */
.lesson-block-label { display: none; }
.lesson-example-prompt, .lesson-activity-prompt { margin: 0 0 14px; }
.lesson-example-steps { counter-reset: example-step; list-style: none; padding: 0 !important; margin: 14px 0 !important; }
.lesson-example-steps li { position: relative; padding: 0 0 14px 38px; margin: 0; color: var(--text-dim); }
.lesson-example-steps li::before { content: counter(example-step); counter-increment: example-step; position: absolute; left: 0; top: 1px; width: 24px; height: 24px; display: grid; place-items: center; border: 1px solid var(--border-2); border-radius: 50%; color: var(--text-dim); font-family: var(--mono); font-size: 11px; line-height: 1; }
.lesson-example-result { margin-top: 10px; padding: 11px 13px; border: 1px solid var(--border-2); border-radius: var(--radius); background: var(--surface); color: var(--text); }
.lesson-example-takeaway { margin: 12px 0 0; font-size: 15px; }

/* Accessible comparison tables */
.lesson-table-wrap { width: 100%; margin: 22px 0; overflow-x: auto; border: 1px solid var(--border); border-radius: var(--radius); background: rgba(255,255,255,0.02); }
.lesson-table-wrap:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.lesson-table { width: 100%; min-width: 540px; border-collapse: collapse; line-height: 1.5; }
.lesson-table caption { padding: 14px 16px; text-align: left; color: var(--text); font-weight: 650; border-bottom: 1px solid var(--border); }
.lesson-table th, .lesson-table td { padding: 12px 16px; text-align: left; vertical-align: top; border-bottom: 1px solid var(--rule); }
.lesson-table th { color: var(--text); background: rgba(255,255,255,0.035); font-size: 14px; }
.lesson-table td { color: var(--text-dim); font-size: 15px; }
.lesson-table tbody tr:last-child td { border-bottom: 0; }

/* Interactive practice */
.lesson-activity { border-color: rgba(121,201,145,0.36); background: rgba(121,201,145,0.045); }
.lesson-activity.is-complete { border-color: var(--bull); }
.activity-choices { display: grid; gap: 9px; margin-top: 14px; }
.activity-choice { display: flex; width: 100%; align-items: flex-start; gap: 11px; padding: 12px 14px; border: 1px solid var(--border-2); border-radius: var(--radius); background: var(--bg-2); color: var(--text); cursor: pointer; font: inherit; line-height: 1.5; text-align: left; transition: border-color .18s, background .18s; }
.activity-choice:hover:not(:disabled) { border-color: var(--accent); background: rgba(121,201,145,0.06); }
.activity-choice:focus-visible, .activity-check:focus-visible, .activity-reflection-reveal:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.activity-choice:disabled { cursor: default; opacity: 1; }
.activity-choice.is-correct { border-color: var(--bull); background: rgba(90,169,126,0.11); }
.activity-choice.is-wrong { border-color: var(--bear); background: rgba(207,91,80,0.1); }
.activity-choice-marker { flex: 0 0 25px; width: 25px; height: 25px; display: grid; place-items: center; border: 1px solid var(--border-2); border-radius: 7px; color: var(--text-dim); font-family: var(--mono); font-size: 11px; }
.activity-choice.is-correct .activity-choice-marker { border-color: var(--bull); color: var(--bull); }
.activity-choice.is-wrong .activity-choice-marker { border-color: var(--bear); color: var(--bear); }
.activity-choice-text { padding-top: 1px; }

.activity-number-form > label, .activity-reflection-label { display: block; margin: 14px 0 7px; color: var(--text); font-size: 15px; font-weight: 600; }
.activity-number-input { display: flex; align-items: center; gap: 9px; max-width: 360px; padding: 0 12px; border: 1px solid var(--border-2); border-radius: var(--radius); background: var(--bg-2); }
.activity-number-input:focus-within { border-color: var(--accent); }
.activity-number-input span { color: var(--text-dim); font-weight: 600; }
.activity-number-input input { border: 0; padding-inline: 0; background: transparent; }
.activity-number-input input:focus { border: 0; }
.activity-number-input input.is-correct { color: var(--bull); }
.activity-number-input input.is-wrong { color: var(--bear); }

.activity-check, .activity-reflection-reveal { display: inline-flex; align-items: center; justify-content: center; min-height: 44px; margin-top: 12px; padding: 10px 16px; border: 1px solid var(--border-2); border-radius: var(--radius); background: var(--surface-2); color: var(--text); cursor: pointer; font-family: var(--font); font-size: 14px; font-weight: 600; transition: border-color .18s, background .18s; }
.activity-check:hover, .activity-reflection-reveal:hover:not(:disabled) { border-color: var(--accent); background: rgba(121,201,145,0.09); }
.activity-reflection-reveal:disabled { cursor: not-allowed; opacity: .45; }
.activity-hint { margin-top: 12px; color: var(--text-dim); font-size: 15px; }
.activity-hint summary { width: fit-content; cursor: pointer; color: var(--amber); }
.activity-hint p { margin: 5px 0 0; }

.activity-match-grid { display: grid; gap: 10px; margin-top: 14px; }
.activity-match-row { display: grid; grid-template-columns: minmax(150px, .7fr) 1.3fr; align-items: center; gap: 14px; padding: 10px 12px; border: 1px solid var(--border); border-radius: var(--radius); background: rgba(0,0,0,0.08); }
.activity-match-row label { color: var(--text); font-size: 15px; font-weight: 600; }
.activity-match-row select { min-width: 0; }
.activity-match-row.is-correct { border-color: var(--bull); background: rgba(90,169,126,0.08); }
.activity-match-row.is-wrong { border-color: var(--bear); background: rgba(207,91,80,0.07); }

.activity-reflection-input { min-height: 120px; }
.activity-help { margin: 5px 0 0; color: var(--text-faint); font-size: 14px; }
.activity-model-answer { margin-top: 14px; padding: 14px 16px; border-left: 3px solid var(--accent); border-radius: 0 9px 9px 0; background: rgba(121,201,145,0.08); }
.lesson-content .activity-model-answer h4 { margin: 0 0 5px; }
.activity-model-answer p { margin: 0; font-size: 15px; }
.activity-feedback { min-height: 0; margin-top: 10px; color: var(--text-dim); font-size: 15px; font-weight: 540; }
.activity-feedback:empty { display: none; }
.activity-feedback.is-correct { color: var(--bull); }
.activity-feedback.is-wrong { color: #e0786f; }

@media (max-width: 620px) {
  .lesson-objectives, .lesson-terms, .lesson-example, .lesson-activity { padding: 16px; }
  .lesson-term, .activity-match-row { grid-template-columns: 1fr; gap: 6px; }
  .lesson-term dd { padding-left: 0; }
  .activity-number-input { max-width: none; }
}

@media (prefers-reduced-motion: reduce) {
  .unit-card, .lesson-item, .quiz-opt, .activity-choice, .activity-check, .activity-reflection-reveal { transition: none; }
}

/* ===================== Interview practice ===================== */
.iv-entry { display: flex; align-items: center; justify-content: space-between; gap: 18px; width: 100%; text-align: left; margin-top: 22px; padding: 22px 24px; border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface); cursor: pointer; transition: border-color .18s; font-family: var(--font); }
.iv-entry:hover { border-color: var(--accent); }
.iv-entry .iv-entry-body h3 { margin: 8px 0 6px; font-size: 19px; }
.iv-entry .iv-entry-body p { color: var(--text-dim); font-size: 14px; line-height: 1.6; max-width: 620px; }
.iv-entry .iv-entry-go { font-size: 26px; color: var(--accent); flex-shrink: 0; }

.iv-diffs { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 16px; }
.iv-diff { padding: 9px 18px; border-radius: 8px; border: 1px solid var(--border-2); background: var(--bg); color: var(--text-dim); cursor: pointer; font-size: 13.5px; font-weight: 600; font-family: var(--font); }
.iv-diff:hover { border-color: var(--accent); color: var(--text); }
.iv-diff.active { background: var(--accent); color: var(--accent-ink); border-color: transparent; }

.iv-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 12px; }
.iv-card { text-align: left; padding: 16px; border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface); cursor: pointer; transition: border-color .15s; font-family: var(--font); }
.iv-card:hover { border-color: var(--accent); }
.iv-card.done { border-color: rgba(121,201,145,0.4); background: rgba(121,201,145,0.05); }
.iv-card-top { display: flex; align-items: center; justify-content: space-between; margin-bottom: 10px; }
.iv-card-title { font-size: 15px; font-weight: 560; color: var(--text); line-height: 1.35; }
.iv-check { font-size: 11px; color: var(--accent); font-family: var(--mono); }
.iv-tier { font-family: var(--mono); font-size: 11px; font-weight: 700; padding: 2px 8px; border-radius: 5px; border: 1px solid var(--border-2); color: var(--text-dim); }
.iv-tier.t-S { color: #e6c765; border-color: rgba(230,199,101,0.4); background: rgba(230,199,101,0.08); }
.iv-tier.t-A { color: var(--accent); border-color: rgba(121,201,145,0.4); background: rgba(121,201,145,0.08); }
.iv-tier.t-B { color: var(--text-dim); }

.iv-detail { padding: 26px; max-width: 760px; }
.iv-detail-head { display: flex; gap: 10px; margin-bottom: 14px; }
.iv-diff-tag { font-family: var(--mono); font-size: 11px; color: var(--text-faint); border: 1px solid var(--border-2); border-radius: 5px; padding: 2px 8px; }
.iv-q-title { font-size: 20px; margin-bottom: 16px; }
.iv-scenario { font-size: 15.5px; line-height: 1.8; color: var(--text); margin-bottom: 16px; }
.iv-question { font-size: 16px; font-weight: 600; color: var(--text); margin-bottom: 18px; }
.iv-options { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
@media (max-width: 560px) { .iv-options { grid-template-columns: 1fr; } }
.iv-opt { padding: 15px 18px; border: 1px solid var(--border-2); border-radius: var(--radius); background: var(--bg-2); color: var(--text); font-size: 14.5px; font-weight: 560; cursor: pointer; font-family: var(--font); line-height: 1.4; transition: border-color .15s, background .15s; }
.iv-opt:hover:not(:disabled) { border-color: var(--accent); }
.iv-opt:disabled { cursor: default; }
.iv-opt.correct { border-color: var(--bull, #5aa97e); background: rgba(90,169,126,0.14); color: var(--text); }
.iv-opt.wrong { border-color: var(--bear, #cf5b50); background: rgba(207,91,80,0.12); }

.iv-reveal { margin-top: 22px; padding-top: 20px; border-top: 1px solid var(--rule); }
.iv-verdict { font-family: var(--serif); font-size: 22px; margin-bottom: 14px; }
.iv-verdict.ok { color: var(--bull, #5aa97e); }
.iv-verdict.no { color: var(--bear, #cf5b50); }
.iv-explanation { color: var(--text-dim); line-height: 1.8; font-size: 15px; }
.iv-explanation h4 { color: var(--accent); font-size: 15px; margin: 20px 0 8px; }
.iv-explanation p { margin: 0 0 12px; }
.iv-explanation strong { color: var(--text); }
.iv-explanation ul { padding-left: 20px; margin: 10px 0; }
.iv-explanation li { margin-bottom: 6px; }
.iv-explanation blockquote { border-left: 3px solid var(--accent); background: rgba(121,201,145,0.06); border-radius: 0 8px 8px 0; padding: 10px 16px; margin: 12px 0; color: var(--text); font-style: italic; }