.flt-shell {
  --course-border: var(--rule);
  --course-soft: #f5f5f5;
  --course-warn: #a1261c;
  max-width: 960px;
  margin: 0 auto;
  padding-bottom: 4rem;
}

.skip-link {
  position: fixed;
  top: -10rem;
  left: 1rem;
  z-index: 100;
  padding: .5rem;
  color: #111;
  background: var(--accent);
}

.skip-link:focus { top: 1rem; }

.course-header {
  padding: 30px 0 0;
}

.course-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.text-button {
  appearance: none;
  padding: 0;
  border: 0;
  color: inherit;
  font: inherit;
  text-decoration: underline;
  background: none;
  cursor: pointer;
}

#course-view { outline: none; }

.course-intro {
  padding-top: 3rem;
}

.course-intro h1,
.lesson-hero h1,
.quiz-heading h1 {
  margin: 0 0 1rem;
  font-size: 28px;
  font-weight: normal;
  line-height: 1.25;
}

.course-intro p,
.lesson-intro {
  max-width: 760px;
  line-height: 1.65;
}

.quiet,
.meta { color: var(--quiet); }
.meta { font-size: 15px; }

.progress-line {
  width: 100%;
  height: 6px;
  margin: .75rem 0 1rem;
  border: 0;
  background: var(--course-border);
}

.progress-line::-webkit-progress-bar { background: var(--course-border); }
.progress-line::-webkit-progress-value { background: var(--accent); }
.progress-line::-moz-progress-bar { background: var(--accent); }

.course-source {
  margin: 1rem 0;
  font-size: 15px;
  line-height: 1.6;
}

.chapter-section { margin: 2rem 0; }
.chapter-section h2 { margin-bottom: .35rem; }
.chapter-section > p { margin-top: 0; }

.unit-list {
  margin: 1.25rem 0;
  padding: 0;
  list-style: none;
}

.unit-row { margin: 0 0 1rem; }
.unit-status { display: inline-block; width: 1.4rem; color: var(--quiet); }
.unit-row.is-complete .unit-status { color: var(--fg); }
.unit-score { color: var(--quiet); font-size: 14px; }
.test-link { margin-top: 1rem; }

.button {
  appearance: none;
  display: inline;
  padding: 0;
  border: 0;
  border-radius: 0;
  color: inherit;
  font: inherit;
  text-decoration: underline;
  background: none;
  cursor: pointer;
}

.button-primary { font-weight: bold; }
.button-danger, .give-up { color: var(--course-warn); }
.button[disabled] { color: var(--quiet); cursor: not-allowed; }

.link-row,
.lesson-actions,
.question-actions,
.result-actions,
.dialog-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  align-items: center;
}

.lesson-wrap,
.quiz-wrap { max-width: 800px; }

.lesson-hero,
.quiz-heading { padding-top: 3rem; }
.breadcrumb { margin: 0 0 2rem; color: var(--quiet); font-size: 15px; }
.breadcrumb span, .breadcrumb a { margin-right: .5rem; }

.lesson-section {
  margin: 2rem 0;
}

.lesson-section h2 { margin-bottom: .75rem; }
.lesson-section p,
.lesson-section li { line-height: 1.75; }
.lesson-section ul { padding-left: 1.4rem; }

.math-panel { line-height: 1.7; }
.lesson-actions { margin: 2rem 0; }

.quiz-topline {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  color: var(--quiet);
  font-size: 15px;
}

.question-card { margin-top: 2rem; }
.question-count { color: var(--quiet); font-size: 15px; }
.question-prompt { margin: 1.5rem 0; font-size: 20px; line-height: 1.6; }

.answer-list { display: grid; gap: 1rem; }
.answer-option { display: grid; grid-template-columns: 1.2rem minmax(0, 1fr); gap: .55rem; align-items: start; cursor: pointer; line-height: 1.5; }
.answer-option input { width: 1rem; height: 1rem; margin-top: .2rem; accent-color: var(--fg); }

.answer-input {
  width: min(100%, 420px);
  box-sizing: border-box;
  padding: .6rem;
  border: 1px solid var(--fg);
  border-radius: 0;
  color: var(--fg);
  font: inherit;
  background: var(--bg);
}

.answer-input:focus { outline: 2px solid var(--accent); outline-offset: 2px; }
.question-actions { margin-top: 1.75rem; }
.question-actions .button-primary { margin-left: auto; }

.feedback-card {
  margin: 1.75rem 0 0;
  padding-left: 1rem;
  border-left: 3px solid var(--course-border);
  line-height: 1.65;
}

.feedback-card.is-correct { border-color: var(--accent); }
.feedback-card.is-wrong { border-color: var(--course-warn); }
.feedback-card h3 { margin: 0 0 .5rem; font-size: 18px; }
.solution-steps { padding-left: 1.5rem; }
.solution-steps li { margin: .5rem 0; }

.result-card { margin-top: 2rem; }
.result-score { margin: 1rem 0; font-size: 42px; }
.result-stats { margin: 1rem 0 2rem; }
.result-stats div { display: inline; margin-right: 1.25rem; }
.result-stats strong { margin-right: .35rem; }

.course-dialog {
  width: min(680px, calc(100% - 2rem));
  max-height: calc(100vh - 2rem);
  box-sizing: border-box;
  padding: 1.5rem;
  overflow-y: auto;
  border: 2px solid var(--fg);
  border-radius: 0;
  color: var(--fg);
  background: var(--bg);
}

.course-dialog::backdrop { background: rgb(0 0 0 / .55); }
.course-dialog h2 { margin-top: 0; font-size: 24px; font-weight: normal; }
.dialog-close { float: right; border: 0; color: inherit; font: inherit; font-size: 24px; background: none; cursor: pointer; }
.dialog-footer { margin-top: 1rem; }
.source-link { display: block; margin: 1rem 0; }
.source-link small { display: block; margin-top: .3rem; color: var(--quiet); }

.help-video {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  margin: 1rem 0;
  border: 1px solid var(--course-border);
}

.notice {
  margin: 1rem 0;
  color: var(--course-warn);
  font-size: 15px;
}

.loading-card { margin: 4rem 0; }

@media (prefers-color-scheme: dark) {
  .flt-shell { --course-soft: #181818; --course-warn: #ff8176; }
}

@media (max-width: 600px) {
  .flt-shell { max-width: none; }
  .course-header { padding-top: 20px; }
  .course-intro, .lesson-hero, .quiz-heading { padding-top: 2rem; }
  .quiz-topline { align-items: flex-start; }
  .question-actions { align-items: flex-start; }
  .question-actions .button-primary { margin-left: 0; }
  .result-stats div { display: block; margin: .5rem 0; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; }
}