* { box-sizing: border-box; }

:root {
  --bg: #0f1220;
  --bg-alt: #171b30;
  --card: #1c2140;
  --accent: #6d5efc;
  --accent-light: #8f83ff;
  --green: #4ade80;
  --red: #ff8b8b;
  --text: #f2f2f6;
  --text-dim: #9a9db0;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

body {
  margin: 0;
  font-family: system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

nav {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 32px;
  background: rgba(15, 18, 32, 0.9);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid #262b4a;
}

nav .brand {
  font-weight: 700;
  color: var(--accent-light);
  letter-spacing: 0.02em;
  cursor: pointer;
}

.nav-progress {
  color: var(--text-dim);
  font-size: 0.85rem;
  font-family: var(--mono);
}

main {
  max-width: 1000px;
  margin: 0 auto;
  padding: 40px 32px 80px;
}

.levels-screen h1 {
  font-size: 2rem;
  margin-bottom: 6px;
}

.sub {
  color: var(--text-dim);
  margin-top: 0;
}

.levels-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 18px;
  margin-top: 28px;
}

.level-card {
  background: var(--card);
  border: 1px solid #262b4a;
  border-radius: 12px;
  padding: 20px;
  cursor: pointer;
  transition: transform 0.15s ease, border-color 0.15s ease;
  position: relative;
}

.level-card.active:hover {
  transform: translateY(-3px);
  border-color: var(--accent);
}

.level-card.locked {
  opacity: 0.45;
  cursor: not-allowed;
}

.level-card.complete {
  border-color: var(--green);
}

.level-badge {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: var(--bg-alt);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  margin-bottom: 12px;
  color: var(--accent-light);
}

.level-card.complete .level-badge {
  background: var(--green);
  color: #0f1220;
}

.level-card h3 {
  margin: 0 0 6px;
  font-size: 1.05rem;
}

.level-card p {
  color: var(--text-dim);
  font-size: 0.85rem;
  margin: 0 0 14px;
  min-height: 40px;
}

.level-progress-bar {
  height: 6px;
  background: var(--bg-alt);
  border-radius: 3px;
  overflow: hidden;
  margin-bottom: 10px;
}

.level-progress-fill {
  height: 100%;
  background: var(--accent);
}

.level-meta {
  display: flex;
  justify-content: space-between;
  font-size: 0.78rem;
  color: var(--text-dim);
}

.exercise-screen {
  max-width: 900px;
}

.back-btn {
  background: none;
  border: none;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.85rem;
  padding: 0;
  margin-bottom: 18px;
}

.back-btn:hover {
  color: var(--text);
}

.kicker {
  color: var(--accent-light);
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 6px;
}

.exercise-screen h1 {
  margin: 0 0 20px;
  font-size: 1.7rem;
}

.concept-cards {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 24px;
}

.concept-card {
  background: var(--bg-alt);
  border: 1px solid #262b4a;
  border-left: 4px solid var(--green);
  border-radius: 10px;
  padding: 16px 20px;
}

.concept-card-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--green);
  font-weight: 700;
  margin-bottom: 8px;
}

.concept-card p {
  margin: 0 0 10px;
  color: var(--text-dim);
}

.concept-example,
.concept-output {
  background: var(--card);
  border: 1px solid #262b4a;
  border-radius: 6px;
  padding: 10px 12px;
  font-family: var(--mono);
  font-size: 0.85rem;
  white-space: pre-wrap;
  margin: 0 0 8px;
}

.concept-output-label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-dim);
  margin-bottom: 4px;
}

.concept-walkthrough {
  margin: 0;
  padding-left: 18px;
  font-size: 0.85rem;
  color: var(--text);
}

.concept-walkthrough li {
  margin-bottom: 6px;
  line-height: 1.45;
}

.concept-walkthrough li:last-child {
  margin-bottom: 0;
}

.learn-block {
  margin-bottom: 28px;
}

.learn-concept-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--green);
  font-weight: 700;
  margin-bottom: 6px;
}

.learn-block h2 {
  margin: 0 0 10px;
  font-size: 1.3rem;
}

.learn-explain {
  color: var(--text-dim);
  margin: 0 0 16px;
  max-width: 640px;
}

.learn-editor {
  flex: 1;
  min-height: 160px;
  background: var(--bg-alt);
  color: var(--text);
  border: none;
  padding: 16px;
  font-family: var(--mono);
  font-size: 0.85rem;
  resize: vertical;
  outline: none;
}

.learn-output {
  flex: 1;
  min-height: 160px;
  margin: 0;
  padding: 16px;
  background: var(--bg-alt);
  white-space: pre-wrap;
  font-family: var(--mono);
  font-size: 0.85rem;
}

.learn-output.error {
  color: var(--red);
}

.learn-run-btn {
  background: var(--accent);
  color: white;
  border: none;
  padding: 6px 14px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
}

.learn-run-btn:hover {
  background: var(--accent-light);
}

.learn-divider {
  border: none;
  border-top: 1px solid #262b4a;
  margin: 28px 0;
}

.message-box {
  background: var(--card);
  border: 1px solid #262b4a;
  border-left: 4px solid var(--accent);
  border-radius: 10px;
  padding: 18px 20px;
  margin-bottom: 24px;
}

.message-box-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-light);
  font-weight: 700;
  margin-bottom: 8px;
}

.message-box p {
  margin: 0;
}

.practice-howto {
  margin-top: 10px !important;
  padding-top: 10px;
  border-top: 1px dashed #33395e;
  color: var(--text-dim);
  font-size: 0.85rem;
}

.hint-btn {
  margin-top: 12px;
  background: transparent;
  border: 1px solid #33395e;
  color: var(--text-dim);
  padding: 6px 12px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8rem;
}

.hint-btn:hover {
  border-color: var(--accent);
  color: var(--text);
}

.hint-text {
  margin-top: 10px;
  color: var(--text-dim);
  font-size: 0.85rem;
  font-style: italic;
}

.playground {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

@media (max-width: 800px) {
  .playground { grid-template-columns: 1fr; }
}

.pane {
  background: var(--card);
  border: 1px solid #262b4a;
  border-radius: 10px;
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.pane-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 14px;
  font-size: 0.8rem;
  color: var(--text-dim);
  border-bottom: 1px solid #262b4a;
  font-family: var(--mono);
}

#runBtn {
  background: var(--accent);
  color: white;
  border: none;
  padding: 6px 14px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
}

#runBtn:hover {
  background: var(--accent-light);
}

#editor {
  flex: 1;
  min-height: 280px;
  background: var(--bg-alt);
  color: var(--text);
  border: none;
  padding: 16px;
  font-family: var(--mono);
  font-size: 0.85rem;
  resize: vertical;
  outline: none;
}

#output {
  flex: 1;
  min-height: 280px;
  margin: 0;
  padding: 16px;
  background: var(--bg-alt);
  white-space: pre-wrap;
  font-family: var(--mono);
  font-size: 0.85rem;
}

#output.error {
  color: var(--red);
}

.result-bar {
  margin-top: 20px;
}

.result {
  padding: 12px 16px;
  border-radius: 8px;
  font-size: 0.9rem;
  margin-bottom: 12px;
}

.result.pass {
  background: rgba(74, 222, 128, 0.12);
  color: var(--green);
  border: 1px solid rgba(74, 222, 128, 0.3);
}

.result.fail {
  background: rgba(255, 139, 139, 0.1);
  color: var(--red);
  border: 1px solid rgba(255, 139, 139, 0.25);
}

.expected {
  background: var(--bg-alt);
  border: 1px solid #262b4a;
  border-radius: 8px;
  padding: 12px 16px;
  font-family: var(--mono);
  font-size: 0.85rem;
  white-space: pre-wrap;
}

.cta {
  background: var(--accent);
  color: white;
  border: none;
  padding: 10px 20px;
  border-radius: 8px;
  cursor: pointer;
  font-weight: 600;
  font-size: 0.9rem;
}

.cta:hover {
  background: var(--accent-light);
}