:root{
  color-scheme:light dark;

  --bg:#F4F2EC;
  --panel:#FAF9F6;
  --panel-hover:#F0EDE4;
  --line:#DFDBD0;
  --line-soft:#E8E5DB;
  --text:#1A1915;
  --muted:#6B675E;
  --accent:#C2603C;
  --accent-soft:rgba(194,96,60,0.09);
  --invert-text:#FAF9F6;

  --serif:ui-serif,Georgia,"Iowan Old Style","Times New Roman",serif;
  --sans:ui-sans-serif,system-ui,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;

  --radius:12px;
  --radius-sm:10px;
  --pill:999px;
  --width:1040px;
}

@media (prefers-color-scheme:dark){
  :root{
    --bg:#1E1D1B;
    --panel:#262522;
    --panel-hover:#2E2D29;
    --line:#3A3730;
    --line-soft:#2C2A26;
    --text:#F2F0EA;
    --muted:#A29D93;
    --accent:#E08A66;
    --accent-soft:rgba(224,138,102,0.12);
    --invert-text:#1E1D1B;
  }
}

*,*::before,*::after{box-sizing:border-box}

body{
  margin:0;
  background:var(--bg);
  color:var(--text);
  font:16px/1.65 var(--sans);
  -webkit-font-smoothing:antialiased;
}

h1,h2,h3,p{margin:0}
ul,ol{margin:0;padding:0;list-style:none}
a{color:inherit}
button{font:inherit;color:inherit;background:none;border:0;margin:0}
::selection{background:var(--accent-soft)}

h1,.q{
  font-family:var(--serif);
  font-weight:400;
  letter-spacing:-0.015em;
  line-height:1.15;
  font-size:clamp(30px,4vw,42px);
}
h2{font-size:19px;line-height:1.35;font-weight:600;letter-spacing:-0.01em}
h3{font-size:16px;line-height:1.45;font-weight:600}

.wrap{max-width:var(--width);margin:0 auto;padding-inline:24px}
#app{display:flex;flex-direction:column;min-height:100vh}
#app main{flex:1 0 auto}
.label{font-size:14px;color:var(--muted)}
.hint{font-size:14px;color:var(--muted)}
.sub{margin-top:14px;font-size:18px;color:var(--muted);max-width:56ch}

:focus-visible{outline:2px solid var(--accent);outline-offset:3px}
main:focus,main:focus-visible{outline:none}

.skip{
  position:absolute;left:24px;top:-60px;z-index:10;
  padding:9px 14px;border-radius:var(--pill);
  background:var(--panel);border:1px solid var(--line);
  font-size:14px;text-decoration:none;
}
.skip:focus{top:14px}

/* Header and footer */
.site-header{border-bottom:1px solid var(--line-soft)}
.site-header .wrap{display:flex;align-items:center;gap:12px;height:64px}
.brand{font-size:16px;font-weight:600;letter-spacing:-0.01em;text-decoration:none}
.header-meta{font-size:14px;color:var(--muted);margin-left:auto}
.site-nav{margin-left:auto;font-size:15px}
.site-nav a{color:var(--muted);text-decoration:none}
.site-nav a:hover,.site-nav a[aria-current="page"]{color:var(--text)}

.site-footer{margin-top:80px;border-top:1px solid var(--line-soft);padding:28px 0}
.site-footer p{font-size:14px;color:var(--muted)}

/* Landing */
.intro{padding-top:72px}
.intro h1{max-width:20ch}
.sample{padding-top:64px}
.sample .q{margin-top:12px;font-size:clamp(24px,2.6vw,30px)}
.options{display:grid;gap:10px;margin-top:22px;max-width:660px}

.option{
  display:flex;gap:12px;align-items:flex-start;width:100%;text-align:left;cursor:pointer;
  padding:14px 16px;
  background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-sm);
  transition:background-color .15s ease,border-color .15s ease;
}
.option:hover{background:var(--panel-hover)}
.option[aria-checked="true"]{border-color:var(--accent);background:var(--accent-soft)}
.option__key{color:var(--muted);font-size:14px;min-width:13px;padding-top:2px}

.sr-only{
  position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;
  clip:rect(0 0 0 0);clip-path:inset(50%);white-space:nowrap;border:0;
}

.used{padding-top:56px}
.used__label{font-size:14px;color:var(--muted)}
.used__list{display:flex;flex-wrap:wrap;align-items:center;gap:24px 36px;margin-top:20px}
.used__list svg{display:block;width:auto;color:var(--muted);opacity:.85}

.block{padding-top:64px}
.block h2+*{margin-top:18px}
.steps{display:grid;gap:14px;max-width:68ch}
.steps li{display:flex;gap:12px}
.steps__n{color:var(--accent);font-size:14px;min-width:14px;padding-top:3px}
.chips{display:flex;flex-wrap:wrap;gap:8px}
.chip{
  display:inline-flex;gap:8px;padding:8px 14px;font-size:15px;text-decoration:none;
  background:var(--panel);border:1px solid var(--line);border-radius:var(--pill);
}
.chip span{color:var(--muted)}
.chip:hover{background:var(--panel-hover)}

/* Tests */
.tests{padding-top:56px}
.tests__head{display:flex;align-items:baseline;justify-content:space-between;gap:16px}
.count{font-size:14px;color:var(--muted)}

.filters{display:flex;flex-wrap:wrap;gap:6px;margin-top:24px}
.filter{
  padding:8px 14px;border-radius:var(--pill);border:1px solid transparent;
  color:var(--muted);font-size:15px;cursor:pointer;
}
.filter:hover{color:var(--text);background:var(--panel-hover)}
.filter[aria-selected="true"]{background:var(--text);border-color:var(--text);color:var(--invert-text)}

.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:16px;margin-top:24px}
.card{
  display:block;height:100%;padding:22px;text-decoration:none;
  background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);
  transition:background-color .15s ease,border-color .15s ease;
}
.card:hover{background:var(--panel-hover);border-color:var(--muted)}
.card__icon{display:block;color:var(--muted);margin-bottom:16px;transition:color .15s ease}
.card__icon svg{display:block}
.card:hover .card__icon{color:var(--text)}
.card p{margin-top:8px;font-size:15px;color:var(--muted)}
.card__meta{display:flex;flex-wrap:wrap;gap:16px;margin-top:18px;font-size:14px;color:var(--muted)}

/* Buttons */
.btn{
  display:inline-block;padding:11px 20px;cursor:pointer;
  border:1px solid var(--line);border-radius:var(--pill);
  background:var(--panel);font-size:15px;text-decoration:none;
  transition:background-color .15s ease,border-color .15s ease,opacity .15s ease;
}
.btn:hover{background:var(--panel-hover)}
.btn--primary{background:var(--text);border-color:var(--text);color:var(--invert-text)}
.btn--primary:hover{background:var(--text);opacity:.86}
.btn--link{background:none;border-color:transparent;color:var(--muted);padding-left:0;padding-right:0}
.btn--link:hover{background:none;color:var(--text);text-decoration:underline}
.btn:disabled{opacity:.4;cursor:not-allowed}
.actions{display:flex;flex-wrap:wrap;align-items:center;gap:20px;margin-top:28px}
.intro .actions{margin-top:32px}

/* Intro and lesson */
.stage{padding-top:40px}
.stage h1{margin-top:20px}
.stage-nav{display:flex;flex-wrap:wrap;gap:20px;font-size:14px}
.stage-nav a{color:var(--muted);text-decoration:none;padding-bottom:5px;border-bottom:2px solid transparent}
.stage-nav a:hover{color:var(--text)}
.stage-nav a[aria-current="step"]{color:var(--text);border-bottom-color:var(--accent)}
.stage-nav__n{margin-right:8px;color:var(--muted)}

.meta-row{display:flex;flex-wrap:wrap;gap:18px;margin-top:20px;font-size:14px;color:var(--muted)}
.cover{display:grid;gap:8px;max-width:60ch}
.cover li{padding-left:20px;position:relative}
.cover li::before{content:"";position:absolute;left:0;top:11px;width:8px;height:1px;background:var(--accent)}

.intro-count{margin-top:18px}

.learn{display:grid;gap:40px;margin-top:36px}
@media (max-width:819px){
  .learn__side{display:none}
}
@media (min-width:820px){
  .learn{grid-template-columns:210px minmax(0,1fr);gap:44px}
  .learn__side{position:sticky;top:28px;align-self:start;max-height:calc(100vh - 56px);overflow:auto}
}
@media (min-width:1100px){
  .learn{grid-template-columns:230px minmax(0,1fr);gap:56px}
}
.learn__side-head{font-size:14px;color:var(--muted);padding-bottom:12px;border-bottom:1px solid var(--line-soft)}
.chapter-list{margin-top:12px;display:grid;gap:2px}
.chapter-list a{display:flex;gap:10px;padding:7px 10px;margin-left:-10px;border-radius:var(--radius-sm);font-size:14px;color:var(--muted);text-decoration:none}
.chapter-list a:hover{background:var(--panel);color:var(--text)}
.chapter-list a[aria-current="page"]{background:var(--panel);color:var(--text);font-weight:500}
.chapter-list__n{color:var(--muted);min-width:16px;text-align:right}

.chapter .label{display:flex;gap:12px;align-items:baseline}
.chapter__back{color:var(--accent);text-decoration:none}
.chapter__back:hover{text-decoration:underline}
.chapter h1{margin-top:10px}
.chapter__body{margin-top:32px;max-width:68ch}
.chapter-nav{display:flex;flex-wrap:wrap;justify-content:space-between;gap:16px;margin-top:44px;padding-top:28px;border-top:1px solid var(--line-soft)}

.chapter-index__head{margin-top:44px;padding-bottom:14px;border-bottom:1px solid var(--line-soft)}
.chapter-index{display:grid}
.chapter-index a{display:flex;gap:18px;padding:18px 0;border-bottom:1px solid var(--line-soft);text-decoration:none}
.chapter-index a:hover .chapter-index__title{color:var(--accent)}
.chapter-index__n{font-size:14px;color:var(--muted);padding-top:3px;min-width:24px}
.chapter-index__body{display:grid;gap:4px}
.chapter-index__title{font-weight:600}
.chapter-index__summary{font-size:15px;color:var(--muted)}

.lesson{margin-top:36px;max-width:68ch}
.lesson__part{padding-bottom:32px}
.lesson__part+.lesson__part{padding-top:32px;border-top:1px solid var(--line-soft)}
.lesson__part p{margin-top:12px}
.lesson__points{display:grid;gap:10px;margin-top:16px}
.lesson__points li{padding-left:20px;position:relative;color:var(--muted)}
.lesson__points li::before{content:"";position:absolute;left:0;top:11px;width:8px;height:1px;background:var(--line)}

/* Test in progress */
.progress{height:3px;background:var(--line-soft)}
.progress__fill{height:3px;background:var(--accent);transition:width .25s ease}
.run{padding-top:56px}
.run .q{margin-top:10px;max-width:26ch}
.run__foot{display:flex;flex-wrap:wrap;align-items:center;gap:20px;margin-top:32px}
.run__hint{margin-top:16px}

/* Result */
.result{padding-top:56px}
.score{display:flex;flex-wrap:wrap;align-items:baseline;gap:12px;margin-top:20px}
.score__num{font-family:var(--serif);font-size:56px;line-height:1.1;letter-spacing:-0.02em}
.score__pct{font-size:15px;color:var(--muted)}
.bar{height:3px;background:var(--line-soft);margin-top:20px;max-width:660px}
.bar__fill{height:3px;background:var(--accent)}

.missed{margin-top:48px;max-width:68ch}
.missed__item{padding:22px 0;border-top:1px solid var(--line-soft)}
.missed__item:first-of-type{margin-top:18px}
.missed__row{margin-top:8px;font-size:15px;color:var(--muted)}
.missed__row span{color:var(--text)}
.missed__note{margin-top:10px;font-size:15px;color:var(--muted)}

/* Empty and error */
.state{padding-top:64px;max-width:58ch}
.state p{margin-top:16px;font-size:18px;color:var(--muted)}

@media (max-width:560px){
  .wrap{padding-inline:20px}
  .intro{padding-top:44px}
  .used,.sample,.block,.tests,.run,.result,.state,.stage{padding-top:32px}
  .site-footer{margin-top:56px}
}

@media (prefers-reduced-motion:reduce){
  *{transition-duration:0.001ms !important}
}