:root {
  --bg: #f8fafc;
  --panel: #ffffff;
  --text: #0f172a;
  --muted: #475569;
  --accent: #16a34a;
  --danger: #dc2626;
  --brand: #2563eb;
  --border: #e2e8f0;
  --shadow: 0 10px 20px rgba(2, 6, 23, 0.06), 0 2px 6px rgba(2, 6, 23, 0.05);
  --yellow: #f59e0b;
  --orange: #f97316;
  --pink: #ec4899;
  --purple: #8b5cf6;
  --blue: #3b82f6;
  --teal: #14b8a6;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen,
    Ubuntu, Cantarell, 'Fira Sans', 'Droid Sans', 'Helvetica Neue', Arial, 'Comic Sans MS', 'Comic Neue', sans-serif;
  background-image: url('/static/img/bg-math.svg'), linear-gradient(0deg, rgba(255,255,255,0.70), rgba(255,255,255,0.70)), url('/static/img/background.jpg');
  background-repeat: repeat, no-repeat, no-repeat;
  background-size: 160px 160px, 100% 100%, cover;
  background-position: 0 0, center center, center center;
  color: var(--text);
}

.app { max-width: 900px; margin: 0 auto; padding: 24px; }

.title { display: flex; align-items: center; gap: 12px; margin: 8px 0 6px; font-size: 28px; font-weight: 900; color: #0f172a; }
.mascot { width: 48px; height: 48px; }
.subtitle { margin: 0 0 18px; color: #64748b; }

.top-bar { display: flex; gap: 12px; align-items: center; }
.timer, .progress { background: var(--panel); padding: 10px 14px; border-radius: 10px; color: var(--muted); border: 1px solid var(--border); box-shadow: var(--shadow); }
.start { margin-left: auto; padding: 10px 16px; border-radius: 10px; border: 1px solid var(--border); background: var(--panel); color: #0f172a; cursor: pointer; box-shadow: var(--shadow); font-size: large;}
.start:hover { background: #f1f5f9; }
.start:disabled { opacity: 0.6; cursor: not-allowed; }

.status { min-height: 22px; margin: 10px 0 8px; color: var(--muted); text-align: center; font-size: xx-large}

.game { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; padding: 28px; box-shadow: var(--shadow); margin-top: 1em;}
.problem { text-align: center; font-size: 72px; font-weight: 900; letter-spacing: 1px; margin: 10px 0 24px; color: #0f172a; background: linear-gradient(120deg, #fef3c7, #e0f2fe); border-radius: 14px; padding: 16px; border: 1px solid var(--border); }
.options { display: grid; grid-template-columns: repeat(2, 1fr); gap: 16px; }

.option-btn { font-size: 28px; font-weight: 800; padding: 22px; border-radius: 14px; border: 1px solid var(--border); background: #ffffff;
  color: #0f172a; cursor: pointer; transition: transform 80ms ease, background 0.2s ease, box-shadow 0.2s ease; box-shadow: var(--shadow); position: relative; overflow: hidden; }
.option-btn:hover { transform: translateY(-1px); }
.option-btn:active { transform: translateY(0); }
.option-btn:disabled { opacity: 0.8; cursor: default; transform: none; }
.option-btn.correct { outline: 2px solid var(--accent); box-shadow: 0 0 0 6px rgba(22,163,74,0.12), var(--shadow); animation: pop 280ms ease-out; }
.option-btn.wrong { outline: 2px solid var(--danger); box-shadow: 0 0 0 6px rgba(220,38,38,0.12), var(--shadow); animation: shake 300ms ease-in-out; }

/* Fun color variants */
.option-btn.c-yellow { background: linear-gradient(180deg, #fff7ed, #fffbeb); border-color: #fde68a; }
.option-btn.c-orange { background: linear-gradient(180deg, #fff1ec, #fff7ed); border-color: #fdba74; }
.option-btn.c-pink { background: linear-gradient(180deg, #fff0f6, #fdf2f8); border-color: #f9a8d4; }
.option-btn.c-purple { background: linear-gradient(180deg, #f5f3ff, #f3e8ff); border-color: #c4b5fd; }
.option-btn.c-blue { background: linear-gradient(180deg, #eff6ff, #e0f2fe); border-color: #93c5fd; }
.option-btn.c-teal { background: linear-gradient(180deg, #ecfeff, #e6fffb); border-color: #99f6e4; }
.option-btn.c-yellow:hover { background: linear-gradient(180deg, #fff3d6, #fff3da); }
.option-btn.c-orange:hover { background: linear-gradient(180deg, #ffe8e1, #ffefe6); }
.option-btn.c-pink:hover { background: linear-gradient(180deg, #ffe7f0, #ffe9f3); }
.option-btn.c-purple:hover { background: linear-gradient(180deg, #efeaff, #eee4ff); }
.option-btn.c-blue:hover { background: linear-gradient(180deg, #e7f0ff, #d9ecfb); }
.option-btn.c-teal:hover { background: linear-gradient(180deg, #e6fcff, #e0fef7); }

.result { margin-top: 18px; padding: 18px; background: var(--panel); border: 1px solid var(--border); border-radius: 14px; box-shadow: var(--shadow); }
.result .score { font-size: 20px; margin-bottom: 8px; }
.again { margin-top: 1em; padding: 10px 16px; border-radius: 10px; border: 1px solid var(--border); background: var(--panel); color: #0f172a; cursor: pointer; box-shadow: var(--shadow); }
.again:hover { background: #f1f5f9; }

.hidden { display: none; }

/* Animations */
@keyframes pop {
  0% { transform: scale(1); }
  50% { transform: scale(1.08); }
  100% { transform: scale(1); }
}

@keyframes shake {
  0% { transform: translateX(0); }
  20% { transform: translateX(-6px); }
  40% { transform: translateX(6px); }
  60% { transform: translateX(-4px); }
  80% { transform: translateX(4px); }
  100% { transform: translateX(0); }
}

.fx-layer { position: fixed; inset: 0; pointer-events: none; overflow: hidden; z-index: 999; }
.confetti { position: absolute; width: 8px; height: 14px; border-radius: 2px; will-change: transform, opacity; transform: translate(-50%, -50%); }
@keyframes confetti {
  0% { opacity: 1; transform: translate(0, 0) rotate(0deg); }
  100% { opacity: 0; transform: translate(var(--tx), var(--ty)) rotate(var(--rot)); }
}

/* Full-screen flash for correct answer */
.flash { position: absolute; inset: 0; background: radial-gradient(circle at 50% 50%, rgba(255,255,255,0.65), rgba(255,255,255,0.0) 60%); animation: flashFade 520ms ease-out forwards; }
@keyframes flashFade { from { opacity: 1; } to { opacity: 0; } }

/* Decorative images */
/* decorative assets removed */

@keyframes float { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-8px); } }
@keyframes twinkle { 0%, 100% { transform: scale(1); opacity: 0.8; } 50% { transform: scale(1.08); opacity: 1; } }

@media (max-width: 640px) {
  .problem { font-size: 52px; }
  .option-btn { font-size: 22px; padding: 18px; }
}