:root {
  --bg: #0f172a;
  --panel: #1e293b;
  --text: #f1f5f9;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --ok: #22c55e;
  --bad: #f43f5e;
  --warn: #fbbf24;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: Georgia, "Times New Roman", serif;
  color: var(--text);
  background:
    radial-gradient(ellipse at 20% 0%, rgba(56, 189, 248, 0.18), transparent 45%),
    linear-gradient(180deg, #0f172a, #111827);
}

body[data-theme="pissarra"] {
  background:
    radial-gradient(ellipse at 50% 0%, rgba(134, 239, 172, 0.35), transparent 50%),
    linear-gradient(180deg, #14532d, #0f172a);
}

body[data-theme="pissarra"] .problem {
  text-shadow: 0 0 18px rgba(134, 239, 172, 0.45);
}

body[data-theme="espai"] {
  background:
    radial-gradient(ellipse at 80% 10%, rgba(192, 132, 252, 0.4), transparent 45%),
    radial-gradient(circle at 20% 80%, rgba(129, 140, 248, 0.25), transparent 40%),
    linear-gradient(180deg, #1e1b4b, #0f172a);
}

body[data-theme="espai"] .problem {
  text-shadow: 0 0 20px rgba(192, 132, 252, 0.55);
}

body[data-theme="candy"] {
  background:
    radial-gradient(ellipse at 20% 0%, rgba(251, 113, 133, 0.4), transparent 45%),
    radial-gradient(circle at 80% 60%, rgba(244, 114, 182, 0.25), transparent 40%),
    linear-gradient(180deg, #4c0519, #0f172a);
}

body[data-theme="quantum"] {
  background:
    radial-gradient(circle at 40% 10%, rgba(34, 211, 238, 0.35), transparent 40%),
    radial-gradient(circle at 70% 70%, rgba(240, 171, 252, 0.3), transparent 40%),
    linear-gradient(180deg, #042f2e, #0f172a);
}

body[data-theme="quantum"] .problem {
  text-shadow: 0 0 22px rgba(34, 211, 238, 0.55), 0 0 36px rgba(240, 171, 252, 0.35);
}

.hidden {
  display: none !important;
}

.header {
  text-align: center;
  padding: 1.4rem 1rem 0.5rem;
}

.header h1 {
  margin: 0.35rem 0;
}

.header p {
  margin: 0;
  color: var(--muted);
}

.back {
  color: var(--muted);
  text-decoration: none;
  font-family: system-ui, sans-serif;
  font-size: 0.9rem;
}

.back:hover {
  color: var(--text);
}

.panel {
  max-width: 480px;
  margin: 0 auto;
  padding: 1.25rem 1rem 2.5rem;
  text-align: center;
}

.panel h2 {
  margin: 0 0 1rem;
}

.panel ul {
  text-align: left;
  color: var(--muted);
  font-family: system-ui, sans-serif;
  line-height: 1.55;
  margin: 0 auto 1.5rem;
  max-width: 380px;
  padding-left: 1.2rem;
}

.panel li {
  margin-bottom: 0.45rem;
}

.primary,
.ghost {
  font-family: system-ui, sans-serif;
  border: none;
  border-radius: 8px;
  padding: 0.7rem 1.2rem;
  cursor: pointer;
  font-weight: 600;
}

.primary {
  background: var(--accent);
  color: #0f172a;
}

.primary:hover {
  filter: brightness(1.06);
}

.ghost {
  margin-top: 1rem;
  background: transparent;
  color: var(--muted);
  text-decoration: underline;
}

.stats {
  display: flex;
  justify-content: center;
  gap: 1.25rem;
  flex-wrap: wrap;
  font-family: system-ui, sans-serif;
  margin-bottom: 1.25rem;
  color: var(--muted);
}

.stats strong {
  color: var(--warn);
}

.timer-wrap {
  position: relative;
  height: 14px;
  background: #0b1220;
  border-radius: 999px;
  overflow: hidden;
  margin-bottom: 0.5rem;
}

.timer-bar {
  height: 100%;
  width: 100%;
  background: linear-gradient(90deg, var(--ok), var(--warn), var(--bad));
  transform-origin: left center;
  transform: scaleX(1);
  transition: transform 0.1s linear;
}

.timer-text {
  display: block;
  margin-bottom: 1.25rem;
  font-family: system-ui, sans-serif;
  font-size: 1.1rem;
  font-weight: 700;
}

.problem {
  font-size: clamp(2rem, 8vw, 3rem);
  font-weight: 700;
  letter-spacing: 0.04em;
  margin: 0.5rem 0 1.25rem;
  font-variant-numeric: tabular-nums;
}

.answer-form {
  display: flex;
  gap: 0.5rem;
  justify-content: center;
  flex-wrap: wrap;
}

.answer-form input {
  width: min(200px, 70vw);
  padding: 0.7rem 0.85rem;
  border-radius: 8px;
  border: 2px solid #334155;
  background: var(--panel);
  color: var(--text);
  font-size: 1.25rem;
  font-family: system-ui, sans-serif;
  text-align: center;
}

.answer-form input:focus {
  outline: none;
  border-color: var(--accent);
}

.feedback {
  min-height: 1.4rem;
  margin: 1rem 0 0;
  font-family: system-ui, sans-serif;
  font-weight: 600;
}

.feedback.ok {
  color: var(--ok);
}

.feedback.bad {
  color: var(--bad);
}