:root{
  --border: #e1e4e8;
  --text: #24292f;
  --muted: #57606a;
  --bg: #f8f9fb;
  --bg-soft: #eef1f5;
  --accent: #2563eb;
  --accent-soft: #2563eb1f;
  --accent-border: #2563eb59;
  --topbar-offset: 6.25rem;
}

@media (prefers-color-scheme: dark){
  :root {
    --border: #2a2a2a;
    --text: #e5e7eb;
    --muted: #9da7b3;
    --bg: #161616;
    --bg-soft: #262626;
    --accent: #3b82f6;
    --accent-soft: #3b82f62e;
    --accent-border: #3b82f673;
    --topbar-offset: 6.25rem;
  }
}

html[data-theme="light"]{
  --border: #e1e4e8;
  --text: #24292f;
  --muted: #57606a;
  --bg: #f8f9fb;
  --bg-soft: #eef1f5;
  --accent: #2563eb;
}


html[data-theme="dark"]{
  --border: #2a2a2a;
  --text: #e5e7eb;
  --muted: #9da7b3;
  --bg: #161616;
  --bg-soft: #262626;
  --accent: #3b82f6;
}

*{ box-sizing: border-box; }

html, body{
  height: 100%;
  margin: 0;
  color: var(--text);
  background: var(--bg);
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;
}

body{
  overflow: hidden;
}

.layout{
  height: 100vh;
  display: grid;

  grid-template-columns: 280px minmax(0, 1fr) 260px;

  max-width: 1400px;
  margin: 0 auto; 
}

.sidebar{
  border-right: 1px solid var(--border);
  padding: 1rem 0.75rem;
  overflow: auto;
  background: var(--bg);
}

.sidebar_header{
  padding: 0.375rem 0.5rem 0.75rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 0.625rem;
}

.sidebar_toptext{
  font-size: 0.75rem;
  color: var(--muted);
  letter-spacing: 0.0125rem;
}

.sidebar_title{
  font-size: 1rem;
  font-weight: 700;
  margin-top: 0.125rem;
}

.sidebar_nav{
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  padding: 0.375rem;
}

.nav_item{
  display: block;
  padding: 0.625rem;
  border-radius: 0.5rem;
  text-decoration: none;
  color: var(--text);
}

.nav_item:hover{
  background: var(--bg-soft);
}

.nav_item.active{
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 600;
  border: 1px solid var(--accent-border);
}

.main{
  scroll-padding-top: var(--topbar-offset);
  overflow: auto;
  padding: 0 1.75rem 2.5rem;
  scrollbar-color: var(--muted) var(--bg-soft);
}

.lesson_nav{
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  display: flex;
  gap: 1rem;
}

.lesson_navBtn{

  text-decoration: none;
  color: var(--text);
  border: 1px solid var(--border);
  background: var(--bg);
  padding: 0.75rem 1rem;
  border-radius: 0.75rem;
  font-weight: 600;
}

.lesson_navBtn:hover{
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 600;
  border: 1px solid var(--accent-border);
  transform: scale(1.05);
}

.lesson_navBtn.prev{ text-align: left; }
.lesson_navBtn.next{ text-align: right; }

.topbar{
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
  padding: 1.25rem 0 0.875rem;
  border-bottom: 1px solid var(--border);
}

.crumbs{
  font-size: 0.75rem;
  color: var(--muted);
  margin-bottom: 0.375rem;
}

h1{
  margin: 0;
  font-size: 1.875rem;
  line-height: 1.15;
}

.subtitle{
  margin: 0.5rem 0 0;
  color: var(--muted);
  max-width: 80ch;
}

.content{
  max-width: 90ch;
  line-height: 1.65;
}

.content h2{
  margin-bottom: 0.625rem;
  font-size: 1.25rem;
}

.content ul{
  padding-left: 1.25rem;
}

.toc{
  border-left: 1px solid var(--border);
  padding: 1rem 0.875rem;
  background: var(--bg);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}


.toc_title{
  font-size: 0.75rem;
  color: var(--muted);
  margin-bottom: 0.625rem;
}

.toc_title-h2 {
  font-size: 0.95rem;
  font-weight: 600;
}

.toc_title-h3 {
  font-size: 0.85rem;
  margin-left: 12px;
  color: var(--muted);
}

.toc_nav{
  flex: 1;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.toc_nav a{
  text-decoration: none;
  color: var(--text);
  font-size: 0.875rem;
  padding: 0.375rem 0.5rem;
  border-radius: 0.5rem;
  line-height: 1.4;
}

.toc_nav a:hover{
  background: var(--bg-soft);
}

.toc_footer{
  margin-top: 1rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--border);
}

.theme_btn{
  width: 100%;
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text);
  padding: 0.5rem 0.75rem;
  border-radius: 0.5rem;
  cursor: pointer;
  font-size: 0.875rem;
  text-align: center;
}

.theme_btn:hover{
  background: var(--bg-soft);
  transform: scale(1.05);
}

.doc_figure{
  max-width: fit-content;
  margin: 2.5rem auto;
  padding: 1rem;
  text-align: center;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 1rem;
}

.doc_figure img{
  max-width: 100%;
  height: auto;
  display: block;
  margin: 0 auto 1rem;
}

.doc_figure--small img{
  max-width: 10rem;
}

.doc_figure--medium img{
  max-width: 25rem;
}

.doc_figure--large img{
  max-width: 100%;
}

.doc_figure figcaption{
  font-size: 0.875rem;
  color: var(--muted);
}

.doc_figure a{
  color: var(--accent);
  text-decoration: none;
}

.doc_figure a:hover{
  text-decoration: underline;
}

.quiz_card {
  margin-top: 2rem;
  padding: 1.25rem;
  border: 1px solid var(--border);
  border-radius: 16px;
  background: var(--bg-soft);
}

.quiz_header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin-bottom: 1rem;
}

.quiz_title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text);
}

.quiz_meta {
  font-size: 0.95rem;
  color: var(--muted);
}

.quiz_question {
  margin-bottom: 1rem;
  font-weight: 600;
  color: var(--text);
}

.quiz_answers {
  display: grid;
  gap: 0.6rem;
}

.quiz_answer {
  display: flex;
  gap: 0.6rem;
  align-items: center;
  padding: 0.7rem 0.9rem;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--bg);
  cursor: pointer;
  transition: 0.15s ease;
}

.quiz_answer:hover {
  border-color: var(--accent-border);
  background: var(--accent-soft);
}

.quiz_answer input {
  accent-color: var(--accent);
}

.quiz_answer.selected {
  border-color: var(--accent);
  background: var(--accent-soft);
}

.quiz_answer.correct {
  border-color: #47c300;
  background: rgba(71, 195, 0, 0.1);
}

.quiz_answer.wrong {
  border-color: #d93025;
  background: rgba(217, 48, 37, 0.1);
}

.quiz_feedback {
  margin-top: 0.8rem;
  font-weight: 600;
}

.quiz_feedback {
  color: var(--text);
}

.quiz_footer{
  display: grid;
  grid-template-columns: 1fr 150px;
  gap: 1rem;
  align-items: center;

  margin-top: 1.2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--bg);
}

.quiz_progressTop{
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin-bottom: .4rem;
}

.quiz_progressLabel{
  color: var(--muted);
  font-size: .95rem;
}

.quiz_progressBar{
  height: 10px;
  border-radius: 999px;
  background: var(--bg);
  border: 1px solid var(--border);
  overflow: hidden;
}

.quiz_progressFill{
  height: 100%;
  background: var(--accent);
  width: 0%;
  transition: width .25s ease;
}

.quiz_btn {
  padding: 0.6rem 1rem;
  border-radius: 10px;
  border: 1px solid var(--accent-border);
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 600;
  cursor: pointer;
  transition: 0.15s ease;
}

.quiz_btn:hover {
  background: var(--accent);
  color: white;
}

.quiz_btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.doc_table{
  width: 100%;
  max-width: 600px;
  margin: 2rem auto;
  border-collapse: separate;
  border-spacing: 0;
  background: var(--bg-soft);
  border: 1px solid var(--accent-border);
  border-radius: 1rem;
  overflow: hidden;
}

.doc_table caption{
  caption-side: top;
  padding: 0.9rem 1rem 0.6rem;
  font-weight: 700;
  font-size: 1rem;
  text-align: left;
  color: var(--text);
}

.doc_table thead{
  background: var(--accent-soft);
}

.doc_table th{
  text-align: left;
  font-weight: 600;
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--accent-border);
  color: var(--accent);
}

.doc_table td{
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--accent-border);
}

.doc_table tbody tr:last-child td{
  border-bottom: none;
}

.doc_table tbody tr:hover{
  background: var(--accent-soft);
  transition: 0.15s ease;
}

.doc_table td:first-child{
  font-weight: 600;
}

.lesson_sources {
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
}

.lesson_sources h3 {
  margin: 0 0 0.75rem 0;
  font-size: 1.05rem;
}

.lesson_sources ul {
  margin: 0;
  padding-left: 1.25rem;
}

.lesson_sources li {
  margin-bottom: 0.45rem;
}

.lesson_sources a {
  color: var(--accent);
  text-decoration: none;
}

.lesson_sources a:hover {
  text-decoration: underline;
}


@media (max-width: 1100px){
  .layout{ grid-template-columns: 280px minmax(0, 1fr); }
  .toc{ display: none; }
}

@media (max-width: 800px){
  body{ overflow: auto; }
  .layout{
    height: auto;
    grid-template-columns: 1fr;
  }
  .sidebar{
    border-right: none;
    border-bottom: 1px solid var(--border);
    max-height: 40vh;
  }
  .main{
    overflow: visible;
    padding: 0 1rem 1.875rem;
  }
  .topbar{
    position: static;
  }
}