:root {
  --bg: #10141c;
  --panel: #171d27;
  --panel-soft: #202939;
  --border: #2e3a4d;
  --text: #eef2f7;
  --muted: #a7b1c2;
  --accent: #2dd4bf;
  --accent-strong: #14b8a6;
  --gold: #f6c453;
  --red: #fb7185;
  --green: #86efac;
  --ink: #0b1220;
  --shadow: 0 14px 34px rgba(3, 7, 18, 0.32);
  --radius: 8px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Inter, "Avenir Next", "Segoe UI", sans-serif;
  background:
    linear-gradient(180deg, rgba(45, 212, 191, 0.12), transparent 22rem),
    var(--bg);
  color: var(--text);
}

button,
input,
select {
  font: inherit;
}

.app-shell {
  width: min(1160px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 2rem 0 3rem;
}

.app-header {
  display: grid;
  grid-template-columns: minmax(0, 1.4fr) minmax(280px, 0.8fr);
  gap: 1rem;
  align-items: stretch;
  margin-bottom: 1rem;
}

.eyebrow {
  margin: 0 0 0.45rem;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

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

h1 {
  margin-bottom: 0.6rem;
  font-size: clamp(2rem, 4vw, 3.1rem);
  line-height: 1.02;
}

h2 {
  margin-bottom: 0.35rem;
  font-size: 1.25rem;
}

.intro,
.supporting-text,
.small-note {
  color: var(--muted);
}

.intro {
  max-width: 62ch;
  margin-bottom: 0.75rem;
  line-height: 1.55;
}

.back-link {
  display: inline-flex;
  min-height: 2.75rem;
  align-items: center;
  color: #ccfbf1;
  font-weight: 700;
}

.formula-card,
.card {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--panel);
  box-shadow: var(--shadow);
}

.formula-card {
  display: flex;
  flex-direction: column;
  justify-content: center;
  padding: 1.1rem;
}

.formula-label,
.panel-label,
.metric-label {
  margin-bottom: 0.35rem;
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.formula {
  margin-bottom: 0.6rem;
  color: var(--gold);
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: clamp(0.9rem, 2vw, 1.1rem);
  font-weight: 800;
}

.formula-note {
  margin-bottom: 0;
  color: #d9e3ee;
  line-height: 1.45;
}

.mode-tabs {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.5rem;
  margin-bottom: 1rem;
}

button {
  min-height: 2.75rem;
  border: 1px solid transparent;
  border-radius: var(--radius);
  padding: 0.7rem 0.95rem;
  background: var(--accent-strong);
  color: #052f2b;
  cursor: pointer;
  font-weight: 800;
  transition: transform 140ms ease, background 140ms ease, border-color 140ms ease;
}

button:hover {
  transform: translateY(-1px);
}

button.secondary,
.tab {
  background: var(--panel-soft);
  color: var(--text);
  border-color: var(--border);
}

.tab.is-active {
  background: #ccfbf1;
  color: #063a35;
  border-color: var(--accent);
}

button:focus,
input:focus,
select:focus {
  outline: 3px solid #5eead4;
  outline-offset: 2px;
}

.workspace,
.practice-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(340px, 0.9fr);
  gap: 1rem;
}

.practice-grid {
  grid-template-columns: minmax(300px, 0.85fr) minmax(0, 1.15fr);
  margin-top: 1rem;
}

.card {
  padding: 1.15rem;
}

.section-heading {
  margin-bottom: 1rem;
}

.solve-row {
  display: grid;
  grid-template-columns: 8rem minmax(0, 1fr);
  gap: 0.75rem;
  align-items: center;
  margin-bottom: 1rem;
}

label {
  font-weight: 800;
}

select,
input[type="number"] {
  width: 100%;
  min-height: 2.75rem;
  border: 1px solid #cad5e2;
  border-radius: var(--radius);
  padding: 0.72rem 0.8rem;
  background: #f8fafc;
  color: var(--ink);
}

.input-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
}

.input-card {
  display: grid;
  gap: 0.65rem;
  min-width: 0;
  padding: 0.9rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--panel-soft);
}

.input-card.is-solved {
  border-color: var(--gold);
  background: rgba(246, 196, 83, 0.1);
}

.input-card.is-solved input[type="number"] {
  background: #fff7df;
}

.input-card.is-solved input {
  cursor: not-allowed;
}

input[type="range"] {
  width: 100%;
  min-height: 2.75rem;
  accent-color: var(--accent);
}

.metric-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.75rem;
  margin-bottom: 1rem;
}

.metric {
  padding: 0.85rem;
  border-radius: var(--radius);
  background: var(--panel-soft);
}

.metric strong {
  display: block;
  font-size: 1.2rem;
}

.bars {
  display: grid;
  gap: 0.85rem;
  margin-bottom: 1rem;
}

.bar-label {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.3rem;
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 700;
}

.bar-track {
  position: relative;
  height: 1rem;
  overflow: hidden;
  border-radius: 999px;
  background: #0d1320;
}

.bar {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  min-width: 2px;
  border-radius: 999px;
}

.bar.driver {
  background: var(--gold);
}

.bar.response {
  background: var(--accent);
}

.interpretation,
.revenue-panel,
.feedback {
  border-radius: var(--radius);
  background: #101722;
  border: 1px solid var(--border);
}

.interpretation {
  margin-bottom: 0.8rem;
  padding: 0.9rem;
  line-height: 1.5;
}

.revenue-panel {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;
  padding: 0.85rem;
}

.revenue-panel p {
  margin-bottom: 0;
}

.hidden {
  display: none;
}

.triangle {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem;
  margin: 1rem 0;
}

.triangle span {
  display: grid;
  min-height: 5.25rem;
  place-items: center;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--panel-soft);
  color: #d1fae5;
  font-family: "SFMono-Regular", Consolas, monospace;
  font-weight: 800;
  text-align: center;
}

.answer-row {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto auto;
  gap: 0.65rem;
  align-items: center;
}

.feedback {
  margin-top: 0.85rem;
  padding: 0.85rem;
  line-height: 1.45;
}

.feedback.correct {
  border-color: rgba(134, 239, 172, 0.7);
  color: var(--green);
}

.feedback.incorrect {
  border-color: rgba(251, 113, 133, 0.7);
  color: #fecdd3;
}

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

@media (max-width: 900px) {
  .app-header,
  .workspace,
  .practice-grid,
  .input-grid {
    grid-template-columns: 1fr;
  }

  .mode-tabs {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 560px) {
  .app-shell {
    width: min(100% - 1rem, 1160px);
    padding-top: 1rem;
  }

  .mode-tabs,
  .answer-row,
  .metric-grid,
  .solve-row,
  .triangle {
    grid-template-columns: 1fr;
  }
}