.secondary-links { display: flex; align-items: center; justify-content: center; gap: 8px; }
.secondary-links .catalog-link { margin-inline: 0; }
html[data-ui="cards"] .practice-topline { margin-bottom: 14px; }
html[data-ui="cards"] .exercise { padding-block: 32px; }
html[data-ui="cards"] .exercise.is-started { justify-content: flex-start; padding-block: 24px; }
html[data-ui="cards"] .exercise.answer-only { justify-content: center; }
html[data-ui="cards"] .exercise.is-started .exercise-level { margin-bottom: 14px; }
html[data-ui="cards"] .exercise.is-started .operation { font-size: calc(40px * var(--formula-scale, 1)); letter-spacing: -.035em; }
html[data-ui="cards"] .exercise.is-started .operation.is-large { font-size: calc(30px * var(--formula-scale, 1)); }
html[data-ui="cards"] .exercise.is-started .operation.is-symbolic { font-size: calc(29px * var(--formula-scale, 1)); letter-spacing: normal; }
html[data-ui="cards"] .think-prompt { display: block; flex: none; text-align: center; margin: 26px 0 0; }
html[data-ui="cards"] .solution { animation: none; }
html[data-ui="cards"] .steps-header { padding: 30px 0 18px; }
html[data-ui="cards"] .result-wrap { padding: 28px 0 0; }
html[data-ui="cards"] .answer-only .result-wrap { padding-top: 18px; }
html[data-ui="cards"] .step { overflow: visible; }
html[data-ui="cards"] .action-hint { display: none; }
html[data-ui="cards"] .practice-footer { padding-top: 14px; }
html[data-ui="cards"] .primary-button.is-revealing { background: var(--accent); color: white; cursor: wait; opacity: .75; }
@media (max-width: 640px) {
  html[data-ui="cards"] .practice-topline { margin-bottom: 8px; }
  html[data-ui="cards"] .exercise.is-started { padding-top: 22px; padding-bottom: 20px; }
  html[data-ui="cards"] .exercise.is-started .operation { font-size: calc(33px * var(--formula-scale, 1)); }
  html[data-ui="cards"] .exercise.is-started .operation.is-large { font-size: calc(26px * var(--formula-scale, 1)); }
  html[data-ui="cards"] .exercise.is-started .operation.is-symbolic { font-size: calc(27px * var(--formula-scale, 1)); }
  html[data-ui="cards"] .steps-header { padding-top: 24px; padding-bottom: 12px; }
  html[data-ui="cards"] .result-wrap { padding-top: 22px; }
  html[data-ui="cards"] .think-prompt { margin-top: 24px; }
}
@media (max-height: 690px) and (max-width: 640px) {
  html[data-ui="cards"] .practice { padding-top: 10px; }
  html[data-ui="cards"] .practice-topline { margin-bottom: 2px; }
  html[data-ui="cards"] .exercise { padding-block: 20px; }
  html[data-ui="cards"] .exercise.is-started { padding-top: 18px; }
}

.card-deck { display: flex; flex-direction: column; flex: 1; min-height: 0; }
.stack-preview { display: none; }
.practice-controls { display: contents; }
.mode-switch { display: none; }
html[data-ui="cards"] .practice-controls {
  display: flex; align-items: center; justify-content: space-between;
  flex: none; gap: 12px; min-height: 44px; margin-bottom: 4px;
}
html[data-ui="cards"] .current-category { min-width: 0; gap: 8px; padding-inline: 0 4px; }
html[data-ui="cards"] .current-category .category-symbol { flex-shrink: 0; }
html[data-ui="cards"] #category-label { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
html[data-ui="cards"] .mode-switch {
  display: flex; align-items: center; justify-content: flex-end; gap: 8px;
  min-width: 92px; min-height: 44px; border: 0; background: transparent;
  padding: 0; font-size: 13px; font-weight: 550; color: var(--muted);
}
.mode-switch[aria-checked="true"] { color: var(--accent) !important; }
.switch-track { position: relative; width: 44px; height: 26px; flex: none; border-radius: 20px; background: #c9cdd9; transition: background .22s ease; }
.switch-thumb { position: absolute; top: 2px; left: 2px; width: 22px; height: 22px; border-radius: 50%; background: #fff; box-shadow: 0 1px 3px #20233026; transition: transform .24s cubic-bezier(.2,.75,.3,1); }
.mode-switch[aria-checked="true"] .switch-track { background: var(--accent); }
.mode-switch[aria-checked="true"] .switch-thumb { transform: translateX(18px); }
.mode-switch:disabled { opacity: .5; }
.secondary-links { flex-wrap: wrap; column-gap: 6px; row-gap: 0; }
html[data-ui="cards"] .app-shell { overflow-x: clip; }
html[data-ui="cards"] .card-deck {
  position: relative; isolation: isolate; margin: 32px -8px 0; --formula-scale: var(--user-formula-scale, 1);
}
html[data-ui="cards"] .exercise-scroll {
  position: relative; z-index: 3;
  padding-inline: 10px; transform-origin: 50% 0; overflow-anchor: none; overflow: clip; touch-action: pinch-zoom;
  -webkit-touch-callout: none; -webkit-user-select: none; user-select: none;
}
html[data-ui="cards"] .stack-preview {
  display: flex; align-items: center; justify-content: center;
  position: absolute; inset: 0; border-radius: 24px; padding: 24px 10px;
  background: var(--surface); transform-origin: 50% 0; overflow: hidden;
  box-shadow: inset 0 0 0 1px #d9deeb, 0 7px 20px #20233014;
  pointer-events: none; user-select: none; -webkit-user-select: none;
}
html[data-ui="cards"] .stack-preview--near { z-index: 2; transform: translate3d(0,-12px,0) scale(.95); filter: blur(1.5px); opacity: .9; }
html[data-ui="cards"] .stack-preview--far { z-index: 1; transform: translate3d(0,-24px,0) scale(.90); filter: blur(3px); opacity: .72; }
.stack-formula { width: 100%; flex: none; }
html[data-ui="cards"] .is-stack-moving > .exercise-scroll,
html[data-ui="cards"] .is-stack-moving > .stack-preview { will-change: transform, filter, opacity; }
html[data-ui="cards"] .exercise-scroll.stack-outgoing {
  position: absolute; inset: 0; z-index: 4; pointer-events: none; user-select: none;
}
html[data-ui="cards"] .practice-footer { position: relative; z-index: 4; }
html[data-ui="cards"] .steps-header { justify-content: center; gap: 12px; }
html[data-ui="cards"] .step { display: block; padding-inline: 14px; text-align: center; }
html[data-ui="cards"] .step-number { display: none; }
html[data-ui="cards"] .step-equation { display: flex; justify-content: center; gap: 6px; }
html[data-ui="cards"] .step-expression { text-align: center; overflow-wrap: normal; }
html[data-ui="cards"] .step-relation,
html[data-ui="cards"] .step-value { flex: none; text-align: center; }
html[data-ui="cards"] .step-equation.is-flow { display: block; }
html[data-ui="cards"] .exercise { height: 100%; min-height: 0; }
html[data-ui="cards"] .solution { flex: none; min-width: 0; }
html[data-ui="cards"] .steps { grid-template-columns: minmax(0, 1fr); }
html[data-ui="cards"] .step { min-width: 0; }
html[data-ui="cards"] .exercise.is-started { padding-block: 12px; justify-content: center; }
html[data-ui="cards"] .exercise.is-started .exercise-level { display: none; }
html[data-ui="cards"] .steps-header { padding: 22px 0 6px; }
html[data-ui="cards"] .step { padding-block: 6px; margin-block: 0; }
html[data-ui="cards"] .result-wrap { padding: 12px 0 0; }
html[data-ui="cards"] .result { min-width: 0; }
html[data-ui="cards"] .think-prompt { margin-top: 10px; }
.step-pages { display: flex; align-items: center; justify-content: center; gap: 12px; margin-top: 4px; color: var(--muted); font-size: 12px; }
.step-pages button { width: 44px; height: 44px; border: 0; border-radius: 10px; background: var(--accent-soft); color: var(--accent); font-size: 23px; }
.step-pages button:disabled { background: transparent; color: #b6bdcf; }
.formula-settings { padding: 6px 6px 14px; margin-bottom: 10px; border-bottom: 1px solid var(--line); }
.formula-settings-heading { display: flex; justify-content: space-between; gap: 12px; font-size: 14px; font-weight: 540; }
.formula-settings output { color: var(--muted); font-size: 13px; font-variant-numeric: tabular-nums; }
.formula-size-control { display: flex; align-items: center; gap: 12px; min-height: 48px; }
.formula-size-control > span { font-size: 12px; color: var(--muted); }
.formula-size-control > span:nth-of-type(2) { font-size: 20px; }
.formula-size-control input { width: 100%; min-width: 0; min-height: 44px; margin: 0; accent-color: var(--accent); }
.formula-size-control button { flex: none; border: 0; min-height: 44px; background: transparent; color: var(--accent); font-size: 13px; padding: 0 3px; }
@media (max-width: 640px) {
  html[data-ui="cards"] .practice { padding-top: 0; }
}
@media (max-height: 690px) and (max-width: 640px) {
  html[data-ui="cards"] .step { padding-block: 2px; }
  html[data-ui="cards"] .steps-header { padding-block: 16px 4px; }
  html[data-ui="cards"] .result-wrap { padding-top: 8px; }
  html[data-ui="cards"] .think-prompt { margin-top: 8px; }
}
.category-picker {
  position: fixed; inset: auto; z-index: 50; margin: 0; padding: 12px;
  border: 1px solid #e3e7f1; border-radius: 20px; background: #fcfdff;
  color: var(--ink); box-shadow: 0 12px 40px #20233024, 0 2px 6px #2023300c;
  touch-action: none; user-select: none; -webkit-user-select: none; -webkit-touch-callout: none;
}
.category-wheel-window { position: relative; height: 100%; overflow: hidden; }
.category-wheel-track { will-change: transform; }
.category-wheel-option {
  display: flex; align-items: center; justify-content: center; height: 44px;
  padding-inline: 16px; font-size: 20px; font-weight: 500; line-height: 1.2;
  white-space: nowrap; cursor: pointer; transform-origin: center;
}
.category-wheel-option[aria-selected="true"] { color: var(--accent); font-weight: 600; }
.category-wheel-marker { position: absolute; top: 50%; left: 2px; transform: translateY(-50%); font-size: 26px; color: var(--accent); pointer-events: none; }
.category-picker.is-cancelled .category-wheel-window { opacity: .3; }
@media (prefers-reduced-motion: reduce) {
  html[data-ui="cards"] .stack-preview { filter: none; }
  .category-wheel-track { will-change: auto; }
}