.sr-only {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  z-index: 100;
  inset-block-start: 8px;
  inset-inline-start: 8px;
  padding: 0.75rem 1rem;
  transform: translateY(-150%);
  border: 2px solid var(--focus);
  border-radius: var(--radius-small);
  background: var(--surface);
  font-weight: 800;
}

.skip-link:focus {
  transform: translateY(0);
}

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  min-block-size: 44px;
  border-radius: var(--radius-small);
  text-decoration: none;
  font-weight: 900;
  letter-spacing: -0.02em;
}

.brand__mark {
  display: inline-grid;
  inline-size: 34px;
  block-size: 34px;
  place-items: center;
  border: 2px solid var(--ink);
  border-radius: 50%;
  background: var(--surface);
  color: var(--accent-strong);
  font-size: 1.3rem;
  line-height: 1;
}

h1,
h2,
p {
  margin-block-start: 0;
}

h1,
h2 {
  text-wrap: balance;
  letter-spacing: -0.035em;
}

h1 {
  margin-block-end: var(--space-3);
  font-size: clamp(2.25rem, 7vw, 4.75rem);
  line-height: 1.08;
}

.game-screen h1,
.summary-screen h1 {
  font-size: clamp(2rem, 6vw, 3.5rem);
}

h2 {
  margin-block-end: var(--space-3);
  font-size: clamp(1.35rem, 3vw, 1.75rem);
  line-height: 1.25;
}

.case-label,
.level-label,
.tutorial-example__number,
.evidence-card__label {
  color: var(--muted);
  font-size: var(--text-small);
  font-weight: 850;
  letter-spacing: 0.06em;
}

.case-label {
  display: inline-block;
  margin-block-end: var(--space-2);
  padding-block-end: 0.15rem;
  border-bottom: 3px solid var(--accent);
  color: var(--accent-strong);
}

.start-screen__lead {
  margin-block-end: 0;
  color: var(--muted);
  font-size: 1.08rem;
}

.tutorial-example {
  padding: var(--space-3);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: rgb(255 255 255 / 86%);
}

.tutorial-example__number {
  display: inline-block;
  margin-block-end: var(--space-2);
}

.tutorial-example .equation-board {
  gap: 0.5rem;
}

.tutorial-example .evidence-card {
  min-block-size: 116px;
  padding: 0.65rem;
  border-radius: var(--radius-small);
  box-shadow: none;
}

.tutorial-example .equation-expression {
  font-size: clamp(1.15rem, 3vw, 1.55rem);
}

.tutorial-example .equals-sign {
  font-size: 1.65rem;
}

.activity-preview {
  padding-block-start: var(--space-3);
  border-top: 1px solid var(--line);
}

.activity-preview li {
  display: flex;
  min-block-size: 58px;
  align-items: center;
  gap: var(--space-2);
  padding: 0.7rem 0;
  border-bottom: 1px solid var(--line);
  font-weight: 750;
}

.activity-preview li span {
  color: var(--accent-strong);
  font-size: var(--text-small);
  letter-spacing: 0.08em;
}

.button {
  display: inline-flex;
  min-inline-size: 10rem;
  min-block-size: 52px;
  align-items: center;
  justify-content: center;
  justify-self: start;
  padding: 0.75rem 1.35rem;
  border: 2px solid transparent;
  border-radius: 999px;
  cursor: pointer;
  font-size: 1rem;
  font-weight: 850;
  line-height: 1.2;
  transition: transform 140ms ease, background-color 140ms ease, border-color 140ms ease;
  scroll-margin-block: var(--space-3) 5rem;
}

.button:not(:disabled):hover {
  transform: translateY(-2px);
}

.button--primary {
  background: var(--accent-strong);
  color: #ffffff;
  box-shadow: 0 8px 20px rgb(169 54 24 / 20%);
}

.button--primary:not(:disabled):hover {
  background: #872810;
}

.button:disabled {
  cursor: not-allowed;
  background: #d9dee3;
  color: #59636d;
  box-shadow: none;
}

.start-button {
  min-inline-size: min(100%, 14rem);
}

.progress-block__labels {
  color: var(--muted);
  font-size: var(--text-small);
  font-weight: 750;
}

progress {
  inline-size: 100%;
  block-size: 12px;
  overflow: hidden;
  border: 0;
  border-radius: 999px;
  background: #e2e8ee;
}

progress::-webkit-progress-bar {
  border-radius: 999px;
  background: #e2e8ee;
}

progress::-webkit-progress-value {
  border-radius: 999px;
  background: var(--accent-strong);
}

progress::-moz-progress-bar {
  border-radius: 999px;
  background: var(--accent-strong);
}

.level-label {
  margin-block-end: 0;
}

.level-label--support {
  color: var(--support);
}

.level-label--core {
  color: var(--core);
}

.level-label--challenge {
  color: var(--challenge);
}

.equation-board {
  padding-block: var(--space-3);
  border-block: 1px solid var(--line);
}

.evidence-card {
  border: 2px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow);
}

.evidence-card__label {
  color: var(--ink);
}

.evidence-card__value {
  color: var(--success);
  font-size: var(--text-small);
}

.equation-expression {
  font-size: clamp(1.55rem, 5vw, 3rem);
  font-weight: 900;
  letter-spacing: -0.04em;
}

.equation-operator {
  color: var(--muted);
}

.equation-term--target {
  display: inline-grid;
  min-inline-size: 1.35em;
  place-items: center;
  border-bottom: 4px solid var(--accent-strong);
  color: var(--accent-strong);
}

.equation-term--repair {
  background: var(--error-soft);
}

.equals-sign {
  color: var(--accent-strong);
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 950;
}

.answer-form legend {
  margin-block-end: var(--space-3);
  padding: 0;
  color: var(--ink);
  font-size: 1.05rem;
  font-weight: 750;
}

.choice {
  position: relative;
  min-inline-size: 0;
}

.choice input {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  opacity: 0;
}

.choice label {
  display: flex;
  min-block-size: 58px;
  align-items: center;
  justify-content: center;
  gap: 0.65rem;
  padding: 0.65rem 0.8rem;
  border: 2px solid var(--line-strong);
  border-radius: var(--radius-small);
  background: var(--surface);
  cursor: pointer;
  font-weight: 850;
  text-align: center;
  transition: border-color 140ms ease, background-color 140ms ease;
}

.choice__indicator {
  inline-size: 18px;
  block-size: 18px;
  flex: 0 0 auto;
  border: 2px solid var(--line-strong);
  border-radius: 50%;
  background: var(--surface);
  box-shadow: inset 0 0 0 4px var(--surface);
}

.choice input:focus-visible + label {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

.choice input:checked + label {
  border-color: var(--accent-strong);
  background: var(--accent-soft);
  color: var(--accent-strong);
}

.choice input:checked + label .choice__indicator {
  border-color: var(--accent-strong);
  background: var(--accent-strong);
}

.choice input:disabled + label {
  cursor: default;
  opacity: 0.78;
}

@media (max-width: 420px) {
  h1 {
    font-size: clamp(2rem, 12vw, 3rem);
  }

  .equation-expression {
    font-size: clamp(1.35rem, 6.8vw, 1.75rem);
  }

  .evidence-card__label,
  .evidence-card__value {
    font-size: var(--text-small);
  }

  .button {
    inline-size: 100%;
  }

  .tutorial-example {
    padding: var(--space-2);
  }

  .tutorial-example__number {
    margin-block-end: var(--space-1);
  }

  .tutorial-example .equation-board {
    padding-block: var(--space-1);
  }

  .tutorial-example .evidence-card {
    min-block-size: 92px;
    padding: 0.4rem;
  }
}