:root {
  --canvas: #f3ecdf;
  --ink: #1f2a2e;
  --muted: #5b645f;
  --panel: rgba(255, 252, 245, 0.94);
  --panel-strong: #fffdf8;
  --accent: #155e63;
  --line: rgba(31, 42, 46, 0.12);
  --success: #24613a;
  --danger: #8d2f2f;
  font-family: Georgia, "Times New Roman", serif;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(21, 94, 99, 0.16), transparent 28%),
    radial-gradient(circle at right, rgba(183, 111, 49, 0.16), transparent 24%),
    linear-gradient(180deg, #f8f3e9 0%, #efe4d1 100%);
}

* {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  min-height: 100vh;
  padding: max(12px, env(safe-area-inset-top)) max(12px, env(safe-area-inset-right)) max(18px, env(safe-area-inset-bottom)) max(12px, env(safe-area-inset-left));
}

button,
input,
textarea,
select {
  font: inherit;
}

.study-app {
  width: min(1180px, 100%);
  margin: 0 auto;
  display: grid;
  gap: 14px;
}

.hero,
.card,
.tab-panel {
  border: 1px solid var(--line);
  border-radius: 20px;
  background: var(--panel);
  box-shadow: 0 18px 42px rgba(63, 44, 24, 0.08);
}

.hero {
  padding: 20px;
}

.hero-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 14px;
  align-items: center;
  justify-items: center;
  text-align: center;
}

.hero-art {
  width: 112px;
  height: 112px;
  border-radius: 20px;
  object-fit: cover;
  object-position: center top;
  border: 1px solid var(--line);
  box-shadow: 0 12px 24px rgba(63, 44, 24, 0.18);
}

.hero-copy {
  min-width: 0;
}

.hero-copy .lede {
  max-width: 34ch;
  margin-left: auto;
  margin-right: auto;
}

.eyebrow {
  margin: 0 0 10px;
  font-size: 0.74rem;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--accent);
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 10px;
  font-size: clamp(1.9rem, 8vw, 3.4rem);
  line-height: 1.02;
}

h2 {
  font-size: clamp(1.2rem, 4.6vw, 1.8rem);
}

h3 {
  font-size: clamp(1rem, 4vw, 1.15rem);
}

.lede {
  max-width: 60ch;
  margin-bottom: 0;
  color: var(--muted);
  font-size: 1rem;
  line-height: 1.5;
}

.tab-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  position: sticky;
  top: 0;
  z-index: 10;
  padding: 4px 0;
  backdrop-filter: blur(10px);
}

.tab-button {
  min-height: 48px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.78);
  color: var(--ink);
  padding: 11px 14px;
  cursor: pointer;
  transition: transform 140ms ease, background-color 140ms ease, color 140ms ease;
  touch-action: manipulation;
}

.tab-button:hover,
.tab-button:focus-visible {
  transform: translateY(-1px);
}

.tab-button.is-active {
  background: var(--accent);
  color: #f9f8f3;
}

.tab-panel {
  display: none;
  padding: 16px;
}

.tab-panel.is-active {
  display: block;
}

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

.card {
  padding: 18px;
}

.prose {
  font-size: 1rem;
  line-height: 1.55;
}

.prose h2 {
  margin-top: 22px;
  margin-bottom: 10px;
}

.prose h3 {
  margin-top: 18px;
  margin-bottom: 8px;
}

.prose ul,
.prose ol,
.summary-panel ul,
.summary-panel ol {
  margin: 0 0 16px;
  padding-left: 20px;
}

.prose li,
.summary-panel li {
  margin-bottom: 8px;
}

.ohms-law-figure {
  margin: 16px 0 18px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #f8f2e7;
}

.ohms-law-figure svg {
  display: block;
  width: 100%;
  height: auto;
}

.ohms-law-strip {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 8px;
  margin-top: 12px;
}

.ohms-law-chip {
  padding: 10px 12px;
  border-radius: 12px;
  background: rgba(21, 94, 99, 0.08);
  font-size: 0.92rem;
  text-align: center;
}

.ohms-law-calculator {
  margin: 14px 0 18px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.72);
}

.ohms-law-calculator p {
  margin-bottom: 12px;
  color: var(--muted);
  line-height: 1.4;
}

.ohms-law-fields {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.ohms-law-field {
  display: grid;
  gap: 6px;
}

.ohms-law-field label {
  font-size: 0.85rem;
  font-weight: 700;
}

.ohms-law-field input {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fffdf8;
}

.ohms-law-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 12px;
}

.ohms-law-result {
  min-height: 1.4em;
  margin: 12px 0 0;
}

.summary-panel {
  align-self: start;
}

.exam-shell {
  display: grid;
  gap: 16px;
}

.exam-intro {
  display: grid;
  gap: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
}

.exam-intro p {
  color: var(--muted);
  margin-bottom: 0;
}

.exam-meta {
  margin-top: 8px;
  font-size: 0.95rem;
}

.exam-copy {
  min-width: 0;
}

.exam-actions {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 10px;
  align-items: stretch;
}

.exam-footer-actions {
  display: flex;
  justify-content: center;
  padding-top: 4px;
}

.action-button {
  min-height: 48px;
  border: none;
  border-radius: 999px;
  padding: 11px 16px;
  cursor: pointer;
  touch-action: manipulation;
}

.action-button.primary {
  background: var(--accent);
  color: #fbfaf4;
}

.action-button.secondary {
  background: #efe4d1;
  color: var(--ink);
}

.score-output {
  grid-column: 1 / -1;
  display: block;
  width: 100%;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.78);
  color: var(--muted);
  line-height: 1.4;
  margin-top: 2px;
}

.score-output:focus {
  outline: 2px solid rgba(21, 94, 99, 0.35);
  outline-offset: 6px;
}

.score-output.is-pass {
  color: var(--success);
  font-weight: 700;
}

.score-output.is-fail {
  color: var(--danger);
  font-weight: 700;
}

.question-list {
  display: grid;
  gap: 12px;
}

.question-card {
  margin: 0;
  min-width: 0;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--panel-strong);
}

.question-card h3 {
  margin-bottom: 12px;
  line-height: 1.35;
}

.option-list {
  display: grid;
  gap: 8px;
}

.option-item {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 11px 12px;
  border: 1px solid transparent;
  border-radius: 12px;
  background: #fbf7ef;
  line-height: 1.4;
}

.option-item input {
  flex: 0 0 auto;
  margin-top: 3px;
}

.feedback {
  min-height: 1.4em;
  margin-top: 12px;
  font-size: 0.95rem;
  font-weight: 600;
  line-height: 1.4;
}

.feedback.correct {
  color: var(--success);
}

.feedback.missed {
  color: var(--danger);
}

@media (min-width: 700px) {
  body {
    padding: 20px;
  }

  .study-app {
    gap: 18px;
  }

  .hero {
    padding: 28px;
  }

  .hero-layout {
    grid-template-columns: 124px minmax(0, 1fr);
    gap: 20px;
    justify-items: stretch;
    text-align: left;
  }

  .hero-art {
    width: 124px;
    height: 124px;
  }

  .hero-copy .lede {
    margin-left: 0;
    margin-right: 0;
    max-width: 60ch;
  }

  .tab-list {
    grid-template-columns: repeat(5, minmax(0, 1fr));
  }

  .tab-panel {
    padding: 22px;
  }

  .guide-grid {
    grid-template-columns: minmax(0, 1.8fr) minmax(280px, 0.9fr);
    gap: 20px;
  }

  .summary-panel {
    position: sticky;
    top: 18px;
  }

  .exam-intro {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto;
    align-items: start;
    column-gap: 16px;
  }

  .exam-actions {
    display: flex;
    flex-wrap: wrap;
    justify-content: flex-end;
    align-items: center;
  }

  .exam-footer-actions {
    justify-content: flex-end;
  }

  .score-output {
    grid-column: 1 / -1;
    margin-top: 0;
  }

  .question-card {
    padding: 16px;
  }
}