/* ==========================================================================
   Sumas y Restas - Estilos amigables para niños
   ========================================================================== */

/* --- Custom Properties (Color Palette) --- */
:root {
  --color-primary: #4a90d9;
  --color-primary-dark: #3570b0;
  --color-secondary: #f5a623;
  --color-accent: #7b61ff;
  --color-correct: #2ecc71;
  --color-correct-bg: #d4f5e0;
  --color-incorrect: #e74c3c;
  --color-incorrect-bg: #fde0dc;
  --color-bg: #f0f4ff;
  --color-card: #ffffff;
  --color-text: #2c3e50;
  --color-text-light: #6b7c93;
  --color-border: #d1dce8;
  --color-config-bg: #f7f8fa;
  --font-main: 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
  --radius: 16px;
  --radius-sm: 10px;
  --shadow: 0 4px 16px rgba(74, 144, 217, 0.12);
  --shadow-btn: 0 3px 8px rgba(74, 144, 217, 0.18);
}

/* --- Reset & Base --- */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: var(--font-main);
  background: linear-gradient(135deg, var(--color-bg) 0%, #e8d8f8 100%);
  color: var(--color-text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 16px;
}

main {
  width: 100%;
  max-width: 540px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}

/* --- Screen Reader Only Utility --- */
.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;
}

/* --- Header --- */
.app-header {
  width: 100%;
  max-width: 540px;
  text-align: center;
  margin-bottom: 8px;
}

.app-header h1 {
  font-size: 2.2rem;
  color: var(--color-primary);
  letter-spacing: 1px;
  margin-bottom: 10px;
  text-shadow: 0 2px 4px rgba(74, 144, 217, 0.12);
}

.score-display {
  display: flex;
  justify-content: center;
  gap: 20px;
  flex-wrap: wrap;
}

.score-item {
  font-size: 1.15rem;
  font-weight: 600;
  padding: 6px 16px;
  border-radius: var(--radius-sm);
  background: var(--color-card);
  box-shadow: var(--shadow);
}

.score-correct-display {
  color: var(--color-correct);
}

.score-incorrect-display {
  color: var(--color-incorrect);
}

#score-correct,
#score-incorrect {
  font-size: 1.3rem;
  font-weight: 700;
}

/* --- Exercise Area --- */
.exercise-area {
  width: 100%;
  background: var(--color-card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 28px 16px;
  text-align: center;
}

.exercise-display {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.exercise-number {
  font-size: 3.2rem;
  font-weight: 700;
  color: var(--color-primary-dark);
  min-width: 56px;
  text-align: center;
}

.exercise-operator {
  font-size: 2.8rem;
  font-weight: 700;
  color: var(--color-secondary);
  min-width: 40px;
  text-align: center;
}

.exercise-equals {
  font-size: 2.8rem;
  font-weight: 700;
  color: var(--color-text-light);
  min-width: 32px;
  text-align: center;
}

.exercise-question {
  font-size: 3.2rem;
  font-weight: 700;
  color: var(--color-accent);
  min-width: 48px;
  text-align: center;
  animation: pulse 1.5s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

/* --- Answer Area --- */
.answer-area {
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
}

.answer-input {
  font-size: 2rem;
  font-weight: 700;
  text-align: center;
  width: 140px;
  padding: 14px 12px;
  border: 3px solid var(--color-border);
  border-radius: var(--radius-sm);
  outline: none;
  color: var(--color-text);
  background: var(--color-card);
  transition: border-color 0.2s;
  -moz-appearance: textfield;
  appearance: textfield;
}

.answer-input::-webkit-outer-spin-button,
.answer-input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.answer-input:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.2);
}

.confirm-btn {
  font-size: 1.4rem;
  font-weight: 700;
  padding: 14px 32px;
  border: none;
  border-radius: var(--radius-sm);
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-accent) 100%);
  color: #fff;
  cursor: pointer;
  box-shadow: var(--shadow-btn);
  transition: transform 0.15s, box-shadow 0.15s;
  letter-spacing: 0.5px;
}

.confirm-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 16px rgba(74, 144, 217, 0.28);
}

.confirm-btn:active {
  transform: translateY(0);
  box-shadow: var(--shadow-btn);
}

/* --- Feedback --- */
.feedback {
  width: 100%;
  text-align: center;
  font-size: 1.5rem;
  font-weight: 700;
  padding: 18px 16px;
  border-radius: var(--radius);
  transition: opacity 0.3s, transform 0.3s;
}

.feedback.hidden {
  display: none;
}

.feedback.correct {
  background: var(--color-correct-bg);
  color: var(--color-correct);
  border: 3px solid var(--color-correct);
  animation: celebrate 0.6s ease;
}

.feedback.incorrect {
  background: var(--color-incorrect-bg);
  color: var(--color-incorrect);
  border: 3px solid var(--color-incorrect);
  animation: shake 0.4s ease;
}

/* --- Celebration Animation (correct answer) --- */
@keyframes celebrate {
  0% { transform: scale(1); }
  20% { transform: scale(1.15) rotate(-3deg); }
  40% { transform: scale(1.1) rotate(3deg); }
  60% { transform: scale(1.12) rotate(-2deg); }
  80% { transform: scale(1.05) rotate(1deg); }
  100% { transform: scale(1) rotate(0deg); }
}

/* --- Shake Animation (incorrect answer) --- */
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20% { transform: translateX(-8px); }
  40% { transform: translateX(8px); }
  60% { transform: translateX(-5px); }
  80% { transform: translateX(5px); }
}

/* --- Separator --- */
.separator {
  width: 100%;
  border: none;
  border-top: 2px dashed var(--color-border);
  margin: 8px 0;
}

/* --- Config Area --- */
.config-area {
  width: 100%;
  background: var(--color-config-bg);
  border-radius: var(--radius);
  padding: 20px 16px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  border: 1px solid var(--color-border);
}

.config-group {
  border: none;
  padding: 0;
}

.config-group legend {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--color-text-light);
  margin-bottom: 8px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.btn-group {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.config-btn {
  font-size: 0.95rem;
  font-weight: 600;
  padding: 8px 18px;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-card);
  color: var(--color-text-light);
  cursor: pointer;
  transition: background 0.2s, color 0.2s, border-color 0.2s;
}

.config-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.config-btn.active {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

/* --- Responsive: Tablets (max-width: 768px) --- */
@media (max-width: 768px) {
  .app-header h1 {
    font-size: 1.8rem;
  }

  .exercise-number {
    font-size: 2.6rem;
  }

  .exercise-operator,
  .exercise-equals {
    font-size: 2.2rem;
  }

  .exercise-question {
    font-size: 2.6rem;
  }

  .answer-input {
    font-size: 1.7rem;
    width: 120px;
    padding: 12px 10px;
  }

  .confirm-btn {
    font-size: 1.2rem;
    padding: 12px 24px;
  }

  .feedback {
    font-size: 1.3rem;
  }
}

/* --- Responsive: Mobile (max-width: 480px) --- */
@media (max-width: 480px) {
  body {
    padding: 10px;
  }

  .app-header h1 {
    font-size: 1.5rem;
  }

  .score-display {
    gap: 10px;
  }

  .score-item {
    font-size: 0.95rem;
    padding: 5px 10px;
  }

  .exercise-area {
    padding: 20px 10px;
  }

  .exercise-number {
    font-size: 2.2rem;
    min-width: 40px;
  }

  .exercise-operator,
  .exercise-equals {
    font-size: 1.8rem;
    min-width: 28px;
  }

  .exercise-question {
    font-size: 2.2rem;
    min-width: 36px;
  }

  .answer-area {
    flex-direction: column;
    gap: 10px;
  }

  .answer-input {
    width: 100%;
    max-width: 200px;
    font-size: 1.5rem;
  }

  .confirm-btn {
    width: 100%;
    max-width: 200px;
    font-size: 1.1rem;
    padding: 14px 20px;
  }

  .feedback {
    font-size: 1.1rem;
    padding: 14px 12px;
  }

  .config-area {
    padding: 14px 10px;
  }

  .btn-group {
    gap: 6px;
  }

  .config-btn {
    font-size: 0.85rem;
    padding: 7px 12px;
  }
}