.op-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem 1rem;
  align-items: end;
  margin-bottom: 0.85rem;
}

.op-field {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}
.op-field label {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.op-field select,
.op-field input {
  font-family: var(--mono);
  font-size: 0.9rem;
  padding: 0.4rem 0.55rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  min-width: 7rem;
}

.op-btns {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin: 0.5rem 0 0.85rem;
}
.op-btns button {
  font-family: var(--mono);
  font-size: 0.85rem;
  padding: 0.4rem 0.55rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  cursor: pointer;
  color: var(--ink);
}
.op-btns button.active {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 18%, var(--surface));
  font-weight: 700;
}

.result-card {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1rem;
  background:
    linear-gradient(160deg, color-mix(in srgb, var(--accent) 7%, var(--surface)), var(--surface) 55%);
  font-family: var(--mono);
}
.result-card .expr {
  font-size: 1.15rem;
  font-weight: 650;
  margin: 0 0 0.5rem;
  word-break: break-word;
}
.result-card .bits {
  font-size: 1.35rem;
  font-weight: 700;
  letter-spacing: 0.06em;
}
.result-card .note {
  margin: 0.5rem 0 0;
  font-size: 0.88rem;
  color: var(--muted);
  font-family: var(--sans, inherit);
}

.compare-row {
  display: grid;
  gap: 0.65rem;
  margin-top: 0.75rem;
}
@media (min-width: 640px) {
  .compare-row {
    grid-template-columns: 1fr 1fr;
  }
}
.compare-pane {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 0.65rem 0.75rem;
  background: var(--surface);
  font-family: var(--mono);
  font-size: 0.88rem;
}
.compare-pane strong {
  display: block;
  margin-bottom: 0.25rem;
}
.compare-pane.diff {
  border-color: color-mix(in srgb, var(--err, #b33) 40%, var(--line));
  background: color-mix(in srgb, var(--err, #b33) 6%, var(--surface));
}

.quiz-choices {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  margin: 0.5rem 0;
}
.quiz-choices label {
  display: flex;
  gap: 0.5rem;
  align-items: flex-start;
  font-family: var(--mono);
  font-size: 0.88rem;
  padding: 0.45rem 0.55rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  cursor: pointer;
}
.quiz-choices label:has(input:checked) {
  outline: 2px solid var(--accent);
  outline-offset: -1px;
}

.op-meta {
  margin: 0.45rem 0 0;
  font-size: 0.88rem;
  color: var(--muted);
}