:root {
  --blue: #3d7bd9;
  --green: #47b26b;
  --bg: #f7f8fb;
  --text: #1f2937;
  --muted: #667085;
  --pill-bg: #ffffff;
}

* { box-sizing: border-box; }

html, body { height: 100%; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  color: var(--text);
  background: var(--bg);
}

/* Capçalera tipus hero com a card */
.app-header { 
  max-width: 1100px; margin: 16px auto; 
  text-align: center; 
  background: #fff; border-radius: 20px; 
  padding: 32px 24px; 
  box-shadow: 0 12px 30px rgba(16,24,40,0.06);
}
.app-header h1 { margin: 0; font-size: 40px; font-weight: 800; letter-spacing: 0.4px; }
.subtitle { margin: 8px 0 0; color: var(--muted); font-size: 16px; }

.container { max-width: 1100px; margin: 0 auto; padding: 16px; }

/* Controls com a card modern */
.controls {
  display: grid;
  grid-template-columns: 1fr 1fr auto;
  gap: 16px;
  align-items: end;
  margin-bottom: 22px;
  background: #fff; border-radius: 20px; padding: 18px 20px;
  box-shadow: 0 12px 30px rgba(16,24,40,0.06);
}
.controls label { display: grid; gap: 6px; font-weight: 600; }
.controls input[type="number"] {
  height: 44px; border: 1px solid #cbd5e1; border-radius: 12px; padding: 0 12px; font-size: 16px; background: #fbfdff;
  transition: box-shadow .15s ease, border-color .15s ease, background .15s ease;
}
.controls input[type="number"]:focus { 
  outline: none; border-color: var(--blue); 
  box-shadow: 0 0 0 4px rgba(61,123,217,0.18);
  background: #fff;
}

.controls button { 
  height: 44px; border: none; border-radius: 12px; 
  background: var(--blue); color: #fff; font-weight: 700; cursor: pointer;
  transition: transform .06s ease, box-shadow .15s ease, opacity .2s ease;
}
.controls button:active { transform: translateY(1px); }
.controls .solution-toggle { align-self: center; font-weight: 500; color: var(--muted); }

.panels { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; }
.panel { background: #fff; border-radius: 16px; padding: 16px; box-shadow: 0 1px 4px rgba(0,0,0,0.06); }
.panel-right { }

.stack { display: grid; gap: 10px; }
.pill {
  border: 3px solid var(--blue);
  border-radius: 18px;
  background: var(--pill-bg);
  padding: 10px 14px;
  max-width: 160px;
}
.number { font-size: 26px; font-weight: 800; letter-spacing: 0.5px; }
.underline { border-bottom: 3px dashed #9cc2f0; margin-top: 6px; }

.green-box {
  border: 6px solid #44a35f;
  border-radius: 20px;
  margin: 12px 0;
  padding: 12px;
  background: #eaf7ef;
}
.step-row { display: grid; grid-template-columns: 1fr 120px auto; gap: 10px; align-items: center; padding: 6px 0; }
.step-row .expr { font-size: 18px; font-weight: 700; }
.step-row input { height: 36px; border-radius: 8px; border: 1px solid #cbd5e1; padding: 0 8px; font-size: 16px; }
.feedback { font-size: 16px; min-width: 24px; }
.feedback.ok { color: #0f766e; }
.feedback.err { color: #b91c1c; }
.hint { color: var(--muted); font-size: 13px; }

.sum-box { margin-top: 6px; }
.sum-row { display: grid; grid-template-columns: 220px auto; gap: 10px; align-items: center; }
#student-total { width: 100%; height: 40px; border-radius: 8px; border: 1px solid #cbd5e1; padding: 0 8px; font-size: 16px; }

.result-pill { border: 4px solid var(--blue); border-radius: 18px; padding: 10px 14px; margin-top: 12px; max-width: 200px; }

.normal-steps { margin-top: 12px; }
.normal-steps .line { display: flex; align-items: center; gap: 10px; }
.normal-steps .value { font-weight: 700; font-size: 18px; }
.normal-steps .step-header { margin-top: 10px; font-weight: 800; color: var(--text); }
.decomp-line { color: var(--muted); font-weight: 700; margin-bottom: 8px; }
.explain { color: var(--muted); margin-top: 16px; }
.footer { text-align: center; padding: 24px; color: var(--muted); }

/* Utilitat per ocultar elements quan no hi ha dades */
.hidden { display: none !important; }

/* Correct/incorrect visuals */
input.correct { border-color: #0f766e; box-shadow: 0 0 0 3px rgba(79, 209, 197, 0.25); }
input.incorrect { border-color: #b91c1c; box-shadow: 0 0 0 3px rgba(244, 63, 94, 0.18); }

/* Responsive */
@media (max-width: 860px) {
  .controls { grid-template-columns: 1fr; }
}

/* Primari vs secundari per destacar el botó de generar */
.controls #generate {
  height: 48px;
  background: linear-gradient(90deg, #6d5efc 0%, #3d7bd9 100%);
  box-shadow: 0 12px 24px rgba(61, 123, 217, 0.25);
  border-radius: 12px;
}
.controls #generate:hover { box-shadow: 0 14px 28px rgba(61, 123, 217, 0.32); }

.controls #toggle-solution-btn {
  background: #fff;
  color: var(--blue);
  border: 1.5px solid #cbd5e1;
  font-weight: 600;
}
.controls #toggle-solution-btn:hover:not(:disabled) {
  background: #f8fafc;
}
.controls #toggle-solution-btn:disabled {
  opacity: 0.6;
  color: #9aa0a6;
  border-color: #e5e7eb;
  cursor: default;
}