:root {
  --ink: #12151d;
  --slate: #454f63;
  --paper: #f3f4f7;
  --accent: #3a35c9;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
  --sans: "IBM Plex Sans", system-ui, sans-serif;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 400 16px/1.6 var(--sans);
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: .75rem 1.25rem;
  background: var(--ink);
}
.topbar-nav { display: flex; align-items: center; gap: 1rem; font-size: 14px; }
.topbar-nav a { color: #c9ccd8; text-decoration: none; }
.topbar-nav a:hover { color: #fff; }
.topbar-nav form { margin: 0; }
.who { font: 400 13px var(--mono); color: #8d93a5; }
.badge { font: 500 11px/1 var(--mono); letter-spacing: .06em; text-transform: uppercase;
  padding: .25rem .4rem; border: 1px solid #3d4457; border-radius: 4px; color: #8f93ff; }
button.link { background: none; border: 0; color: #c9ccd8; cursor: pointer;
  font: 400 14px var(--sans); padding: 0; }
button.link:hover { color: #fff; }

.wordmark {
  font: 500 15px/1 var(--mono);
  letter-spacing: .04em;
  color: #fff;
  text-decoration: none;
}
.wordmark span { color: #8f93ff; }

.pane { max-width: 62rem; margin: 2.5rem auto; padding: 0 1.25rem; }

.eyebrow {
  font: 500 12px/1 var(--mono);
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--slate);
  margin: 0 0 .5rem;
}

h1 { font-size: clamp(1.6rem, 3vw, 2.1rem); line-height: 1.2; margin: 0 0 1rem; }
.muted { color: var(--slate); }
code { font: 400 .9em var(--mono); background: #e6e8ef; padding: .12em .35em; border-radius: 3px; }

.pane.narrow { max-width: 27rem; }
.stack { display: grid; gap: 1rem; }

label { display: grid; gap: .35rem; font-size: 14px; font-weight: 500; }
input[type=email], input[type=password], input[type=text] {
  font: 400 15px var(--sans); padding: .6rem .7rem;
  border: 1px solid #d7dbe4; border-radius: 6px;
  background: #fff; color: var(--ink);
}
input:focus-visible, button:focus-visible, a:focus-visible {
  outline: 2px solid var(--accent); outline-offset: 2px;
}

.btn {
  font: 500 14px var(--sans); cursor: pointer;
  padding: .6rem 1rem; border-radius: 6px;
  border: 1px solid var(--accent); background: var(--accent); color: #fff;
  text-decoration: none; display: inline-block;
}
.btn:hover { background: #302bb0; }

.alert { background: #fdeceb; border-left: 3px solid #9a3324;
  padding: .6rem .8rem; font-size: 14px; margin: 0 0 1rem; }

h2 { font-size: 1.15rem; margin: 2rem 0 .75rem; }

.module { font-size: 1.05rem; margin: 2rem 0 .5rem; padding-bottom: .4rem;
  border-bottom: 1px solid #d7dbe4; }
.lesson-list { list-style: none; margin: 0; padding: 0; }
.lesson-row { display: flex; align-items: baseline; gap: .9rem;
  padding: .7rem .25rem; border-bottom: 1px solid #e6e8ef; }
.lesson-row .idx { font: 500 13px var(--mono); color: #9aa1b1; }
.lesson-row a { color: var(--ink); text-decoration: none; font-weight: 500; flex: 1; }
.lesson-row a:hover { color: var(--accent); }
.tags { display: flex; gap: .4rem; }
.tag { font: 500 11px/1 var(--mono); letter-spacing: .06em; text-transform: uppercase;
  padding: .3rem .45rem; border: 1px solid #d7dbe4; border-radius: 4px; color: var(--slate); }
.tag.done { color: #146b52; border-color: #b6d8cc; }
.reading .prose { max-width: 38rem; }
.prose pre { background: var(--ink); color: #e6e8f0; padding: .9rem 1rem;
  border-radius: 6px; overflow-x: auto; font: 400 13.5px/1.55 var(--mono); }
.prose code { font: 400 .9em var(--mono); background: #e6e8ef;
  padding: .12em .35em; border-radius: 3px; }
.prose pre code { background: none; padding: 0; }
.pager { display: flex; justify-content: space-between; margin: 2.5rem 0 1rem; max-width: 38rem; }
.pager a { color: var(--accent); text-decoration: none; font-size: 14px; }

.split { display: grid; grid-template-columns: minmax(0,1fr) minmax(0,1fr);
  min-height: calc(100vh - 3.1rem); }
.reading { padding: 2rem clamp(1.25rem, 3vw, 2.5rem); overflow-y: auto; }
.lab { display: flex; flex-direction: column; background: var(--ink);
  position: sticky; top: 0; height: calc(100vh - 3.1rem); }
.lab-head { display: flex; align-items: center; justify-content: space-between;
  padding: .6rem .9rem; border-bottom: 1px solid #262c3a; }
.lab-label { font: 500 12px/1 var(--mono); letter-spacing: .12em;
  text-transform: uppercase; color: #8d93a5; }
.btn.small { padding: .35rem .7rem; font-size: 13px; }
.btn[disabled] { opacity: .45; cursor: not-allowed; }
.lab-body { flex: 1; position: relative; }
.lab-empty { position: absolute; inset: 0; display: grid; align-content: center;
  padding: 2rem; text-align: center; color: #c9ccd8; }
.lab-empty .muted { color: #7d8394; font-size: 14px; }
#lab-frame { width: 100%; height: 100%; border: 0; display: block; background: #000; }

@media (max-width: 900px) {
  .split { grid-template-columns: 1fr; }
  .lab { position: static; height: 70vh; }
}