:root {
  --bg: #0f1117;
  --bg-2: #161a23;
  --bg-3: #1d2230;
  --border: #262d3d;
  --text: #dbe2ef;
  --muted: #8b93a7;
  --accent: #4f8cff;
  --green: #22c55e;
  --red: #ef4444;
  --yellow: #f59e0b;
  --mono: "JetBrains Mono", "Fira Code", Consolas, "Liberation Mono", monospace;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  font-size: 15px;
  line-height: 1.55;
}

#topbar {
  height: 52px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
  background: var(--bg-2);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand {
  font-size: 18px;
  font-weight: 800;
  letter-spacing: 0.3px;
}
.brand span { color: var(--accent); }

.topbar-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.status {
  font-size: 12.5px;
  color: var(--muted);
  display: flex;
  align-items: center;
  gap: 7px;
}
.status::before {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--muted);
}
.status.loading::before { background: var(--yellow); }
.status.ready::before { background: var(--green); }
.status.error::before { background: var(--red); }

.btn {
  background: var(--accent);
  border: 1px solid transparent;
  color: #fff;
  border-radius: 8px;
  padding: 7px 14px;
  font-size: 13.5px;
  font-weight: 600;
  cursor: pointer;
  transition: filter .15s;
}
.btn:hover { filter: brightness(1.12); }
.btn:disabled { opacity: .5; cursor: not-allowed; }
.btn.ghost {
  background: transparent;
  border-color: var(--border);
  color: var(--text);
}

#layout {
  display: flex;
  height: calc(100vh - 52px);
}

/* ---------- Sidebar ---------- */

#sidebar {
  width: 310px;
  min-width: 310px;
  overflow-y: auto;
  background: var(--bg-2);
  border-right: 1px solid var(--border);
  padding: 14px 10px 30px;
}

.sidebar-title {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--muted);
  padding: 0 10px 10px;
}

.phase-item {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  padding: 9px 10px;
  border-radius: 10px;
  cursor: pointer;
  border: 1px solid transparent;
  margin-bottom: 3px;
  transition: background .12s;
}
.phase-item:hover { background: var(--bg-3); }
.phase-item.active {
  background: var(--bg-3);
  border-color: var(--border);
}

.phase-num {
  width: 26px;
  height: 26px;
  min-width: 26px;
  border-radius: 7px;
  display: grid;
  place-items: center;
  font-size: 12.5px;
  font-weight: 700;
  color: #0f1117;
  margin-top: 1px;
}

.phase-info { flex: 1; min-width: 0; }

.phase-title {
  font-size: 13.5px;
  font-weight: 700;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.phase-meta {
  font-size: 11.5px;
  color: var(--muted);
  margin-top: 2px;
}

.progress-track {
  height: 4px;
  background: var(--border);
  border-radius: 4px;
  margin-top: 7px;
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  border-radius: 4px;
  background: var(--accent);
  transition: width .3s;
}

/* ---------- Main / views ---------- */

#main {
  flex: 1;
  overflow-y: auto;
  padding: 26px 30px 80px;
  max-width: 980px;
}

.view-header { margin-bottom: 22px; }

.crumb {
  font-size: 12px;
  color: var(--muted);
  margin-bottom: 8px;
  cursor: pointer;
}
.crumb span:hover { color: var(--accent); }

.view-title {
  font-size: 26px;
  font-weight: 800;
  margin: 0 0 6px;
}

.view-goal {
  color: var(--muted);
  font-size: 14px;
  margin: 0;
}

.phase-banner {
  border-radius: 14px;
  padding: 14px 18px;
  margin-bottom: 24px;
  color: #0f1117;
  font-weight: 700;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 14px;
}
.phase-banner small {
  font-weight: 600;
  opacity: .75;
}

.skills {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  margin-bottom: 24px;
}
.skill {
  font-size: 12px;
  padding: 4px 10px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-2);
  color: var(--text);
}

h2.section {
  font-size: 15px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--muted);
  margin: 26px 0 12px;
}

/* lesson cards in phase view */

.lesson-card {
  display: flex;
  align-items: center;
  gap: 12px;
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px 14px;
  margin-bottom: 8px;
  cursor: pointer;
  transition: border-color .12s, background .12s;
}
.lesson-card:hover { border-color: var(--accent); background: var(--bg-3); }

.lesson-idx {
  width: 30px;
  height: 30px;
  min-width: 30px;
  border-radius: 8px;
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: 13px;
}
.lesson-card .lesson-title { flex: 1; font-weight: 600; font-size: 14px; }
.lesson-count { font-size: 12px; color: var(--muted); }
.lesson-done {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  border: 2px solid var(--border);
  display: grid;
  place-items: center;
  font-size: 11px;
  color: #0f1117;
}
.lesson-done.done { background: var(--green); border-color: var(--green); }

/* resources */

.resource {
  display: flex;
  gap: 10px;
  align-items: baseline;
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 14px;
  margin-bottom: 7px;
}
.resource a {
  color: var(--text);
  text-decoration: none;
  font-size: 13.5px;
  font-weight: 600;
}
.resource a:hover { color: var(--accent); }
.resource .r-desc { color: var(--muted); font-size: 12.5px; }

/* ---------- Lesson view ---------- */

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  margin: 30px 0 10px;
}

.kid-box {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: 10px;
  padding: 14px 18px;
  margin-bottom: 24px;
  font-size: 14.5px;
}
.kid-box strong { color: var(--accent); }

.lesson-body {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 24px;
  margin-bottom: 26px;
}

/* markdown */

.lesson-body h1, .lesson-body h2, .lesson-body h3, .lesson-body h4 {
  margin: 22px 0 10px;
  line-height: 1.3;
}
.lesson-body h1 { font-size: 21px; }
.lesson-body h2 { font-size: 18px; }
.lesson-body h3 { font-size: 16px; }
.lesson-body p { margin: 10px 0; }
.lesson-body ul, .lesson-body ol { padding-left: 22px; margin: 10px 0; }
.lesson-body li { margin: 4px 0; }
.lesson-body code {
  font-family: var(--mono);
  font-size: 13px;
  background: var(--bg-3);
  padding: 1.5px 6px;
  border-radius: 5px;
  color: #ffd479;
}
.lesson-body pre {
  background: #14161c;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px 16px;
  overflow-x: auto;
  margin: 14px 0;
}
.lesson-body pre code {
  background: none;
  padding: 0;
  color: var(--text);
  font-size: 13px;
}
.lesson-body blockquote {
  margin: 12px 0;
  padding: 10px 14px;
  background: var(--bg-3);
  border-left: 3px solid var(--yellow);
  border-radius: 0 8px 8px 0;
  color: var(--text);
}
.lesson-body table {
  border-collapse: collapse;
  margin: 14px 0;
  width: 100%;
  font-size: 13.5px;
}
.lesson-body th, .lesson-body td {
  border: 1px solid var(--border);
  padding: 7px 12px;
  text-align: left;
}
.lesson-body th { background: var(--bg-3); }
.lesson-body a { color: var(--accent); }

/* tokens */

.tok-k { color: #c792ea; }
.tok-s { color: #c3e88d; }
.tok-c { color: #6b7382; font-style: italic; }
.tok-v { color: #82aaff; }
.tok-n { color: #f78c6c; }
.tok-tag { color: #ff5370; }
.tok-o { color: #89ddff; }

/* exercises */

.exercise {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 18px 20px;
  margin-bottom: 20px;
}

.ex-head {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}
.ex-num {
  width: 28px;
  height: 28px;
  min-width: 28px;
  border-radius: 8px;
  background: var(--bg-3);
  border: 1px solid var(--border);
  display: grid;
  place-items: center;
  font-size: 13px;
  font-weight: 700;
}
.ex-head h3 { margin: 0; font-size: 15.5px; flex: 1; }
.diff {
  font-size: 11px;
  font-weight: 700;
  padding: 3px 9px;
  border-radius: 999px;
  text-transform: uppercase;
  letter-spacing: .5px;
}
.diff-1 { background: rgba(34,197,94,.15); color: var(--green); }
.diff-2 { background: rgba(245,158,11,.15); color: var(--yellow); }
.diff-3 { background: rgba(244,63,94,.15); color: #fb7185; }
.diff-4 { background: rgba(239,68,68,.2); color: var(--red); }

.ex-stmt { margin: 12px 0; font-size: 14px; }
.ex-stmt code {
  font-family: var(--mono);
  background: var(--bg-3);
  padding: 1px 6px;
  border-radius: 5px;
  font-size: 12.5px;
}

.ex-editor {
  border: 1px solid var(--border);
  border-radius: 0 10px 10px 10px;
  overflow: hidden;
}
.ex-editor .CodeMirror { height: 240px; font-size: 13.5px; }

.filebar {
  display: flex;
  gap: 8px;
  align-items: center;
  margin: 12px 0 0;
  flex-wrap: wrap;
}
.file-tabs {
  display: flex;
  gap: 4px;
  flex-wrap: wrap;
}
.filetab {
  background: var(--bg-3);
  border: 1px solid var(--border);
  border-bottom: none;
  color: var(--muted);
  border-radius: 8px 8px 0 0;
  padding: 6px 12px;
  font-size: 12.5px;
  cursor: pointer;
  font-family: var(--mono);
}
.filetab.active {
  background: var(--bg-2);
  color: var(--text);
  border-color: var(--border);
}
.btn-file-add {
  font-size: 12.5px;
  padding: 5px 10px;
  font-family: var(--mono);
}

.ex-actions {
  display: flex;
  gap: 8px;
  align-items: center;
  margin-top: 12px;
  flex-wrap: wrap;
}
.btn-run { background: var(--green); }
.btn-check { background: var(--accent); }
.btn-solution {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--muted);
}
.btn-solution:hover { color: var(--text); border-color: var(--text); }

.ex-status {
  font-size: 13px;
  font-weight: 700;
  margin-left: 4px;
}
.ex-status.ok { color: var(--green); }
.ex-status.fail { color: var(--red); }

.ex-output {
  display: none;
  background: #14161c;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  font-family: var(--mono);
  font-size: 13px;
  white-space: pre-wrap;
  word-break: break-word;
  margin: 12px 0 0;
  max-height: 260px;
  overflow-y: auto;
}
.ex-output.show { display: block; }
.ex-output .err { color: #ff6b6b; }

/* sandbox */

.sandbox-editor {
  border: 1px solid var(--border);
  border-radius: 10px;
  overflow: hidden;
}
.sandbox-editor .CodeMirror { height: 380px; font-size: 14px; }

.sandbox-output {
  background: #14161c;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px 16px;
  font-family: var(--mono);
  font-size: 13.5px;
  white-space: pre-wrap;
  word-break: break-word;
  margin-top: 14px;
  min-height: 60px;
}
.sandbox-output .err { color: #ff6b6b; }

.empty {
  color: var(--muted);
  border: 1px dashed var(--border);
  border-radius: 12px;
  padding: 26px;
  text-align: center;
}

@media (max-width: 900px) {
  #sidebar { width: 220px; min-width: 220px; }
}