:root {
  --bg: #14141c;
  --bg-panel: #1d1d29;
  --border: #34344a;
  --text: #e6e6ef;
  --text-dim: #9494ab;
  --accent: #ef4a5c;
  --accent-2: #4ac0ef;
  --warn: #f2c14e;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--mono);
  line-height: 1.5;
}

header {
  padding: 2.5rem 1.5rem 1.5rem;
  max-width: 860px;
  margin: 0 auto;
  text-align: center;
}

h1 {
  margin: 0 0 0.5rem;
  font-size: 2.2rem;
  letter-spacing: 0.05em;
  color: var(--accent-2);
}

.tagline {
  color: var(--text-dim);
  max-width: 640px;
  margin: 0 auto;
}

.links {
  margin: 0.75rem 0 0;
  font-size: 0.85rem;
}

.links a {
  color: var(--accent-2);
  text-decoration: none;
}

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

.links span {
  color: var(--border);
  margin: 0 0.5rem;
}

.status {
  display: inline-block;
  margin-top: 1rem;
  padding: 0.35rem 0.9rem;
  border-radius: 4px;
  font-size: 0.85rem;
}

.status.error {
  background: rgba(239, 74, 92, 0.15);
  color: var(--accent);
  border: 1px solid var(--accent);
}

main {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 1.5rem 3rem;
}

.exercise {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.5rem 1.75rem;
  margin-bottom: 2.5rem;
}

.exercise h2 {
  margin-top: 0;
  color: var(--accent-2);
  font-size: 1.15rem;
}

.exercise h2::before {
  content: "\25B8 ";
  color: var(--accent);
}

.exercise p {
  color: var(--text-dim);
}

.exercise code,
.prose code {
  color: var(--warn);
  background: rgba(255, 255, 255, 0.06);
  padding: 0.1rem 0.35rem;
  border-radius: 3px;
}

.prose {
  margin-bottom: 2.5rem;
}

.prose h2 {
  color: var(--text);
  font-size: 1.5rem;
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.6rem;
  margin: 0 0 1.25rem;
}

.prose h3 {
  color: var(--accent-2);
  font-size: 1.05rem;
  margin: 1.75rem 0 0.75rem;
}

.prose p {
  margin: 0 0 1rem;
}

.prose ul,
.prose ol {
  padding-left: 1.4rem;
  margin: 0 0 1rem;
}

.prose li {
  margin-bottom: 0.6rem;
}

.prose a {
  color: var(--accent-2);
}

.prose pre {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1rem 1.1rem;
  margin: 0 0 1rem;
  overflow-x: auto;
  font-size: 0.82rem;
  line-height: 1.55;
}

.prose pre code {
  background: none;
  color: var(--text);
  padding: 0;
  border-radius: 0;
}

.prose table {
  width: 100%;
  border-collapse: collapse;
  margin: 0 0 1.25rem;
  font-size: 0.88rem;
}

.prose th,
.prose td {
  border: 1px solid var(--border);
  padding: 0.5rem 0.75rem;
  text-align: left;
}

.prose th {
  background: var(--bg-panel);
  color: var(--text-dim);
  font-weight: normal;
}

.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  align-items: end;
  margin: 1.25rem 0;
}

.controls label {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  font-size: 0.8rem;
  color: var(--text-dim);
}

.controls input,
.controls select {
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 4px;
  padding: 0.4rem 0.5rem;
  font-family: var(--mono);
  width: 8rem;
}

button {
  background: var(--accent);
  color: #14141c;
  border: none;
  border-radius: 4px;
  padding: 0.55rem 1.1rem;
  font-family: var(--mono);
  font-weight: bold;
  cursor: pointer;
  height: 2.3rem;
}

button:hover {
  filter: brightness(1.1);
}

button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.output {
  margin-top: 1rem;
}

.result-line {
  font-size: 0.95rem;
  white-space: pre-wrap;
  color: var(--text);
}

canvas {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  display: block;
  max-width: 100%;
}

.bit-grid,
.nybble-grid {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.75rem;
}

.byte-row {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.35rem;
}

.byte-label {
  font-size: 0.75rem;
  color: var(--text-dim);
}

.bits {
  display: flex;
  gap: 2px;
}

.bit {
  width: 1.6rem;
  height: 1.6rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border);
  border-radius: 3px;
  font-size: 0.85rem;
  background: var(--bg);
}

.bit.one {
  background: var(--accent-2);
  color: #14141c;
  border-color: var(--accent-2);
}

.nybble {
  display: flex;
  gap: 2px;
}

.nybble.high .bit.one {
  background: var(--accent);
  border-color: var(--accent);
}

.nybble.low .bit.one {
  background: var(--accent-2);
  border-color: var(--accent-2);
}

.hint {
  font-size: 0.82rem;
  color: var(--text-dim);
  border-left: 2px solid var(--border);
  padding-left: 0.75rem;
  margin-top: 1rem;
  margin-bottom: 0;
}

footer {
  max-width: 860px;
  margin: 0 auto;
  padding: 1.5rem;
  text-align: center;
  color: var(--text-dim);
  font-size: 0.8rem;
  border-top: 1px solid var(--border);
}

footer a {
  color: var(--accent-2);
}