* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  background-color: #f5f5f5;
  padding: 20px;
}

.home {
  max-width: 1200px;
  margin: 0 auto;
}

.home h1 {
  text-align: center;
  color: #333;
  margin-bottom: 30px;
  font-size: 2.5rem;
}

.stories-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 20px;
  padding: 20px 0;
}

.story-card {
  background: white;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  transition: transform 0.2s, box-shadow 0.2s;
  cursor: pointer;
  text-decoration: none;
  display: block;
  color: inherit;
  padding: 20px;
  text-align: center;
}

.story-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.session-icon {
  font-size: 3rem;
  margin-bottom: 15px;
}

.story-card h2 {
  font-size: 1.2rem;
  color: #333;
  margin-bottom: 10px;
}

.session-description {
  font-size: 0.9rem;
  color: #666;
  line-height: 1.4;
}

.study-sessions-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 20px;
  padding: 20px 0;
}

.study-session-card {
  background: white;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  transition: transform 0.2s, box-shadow 0.2s;
  cursor: pointer;
  text-decoration: none;
  display: block;
  color: inherit;
}

.study-session-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.study-session-card h2 {
  padding: 15px;
  font-size: 1.2rem;
  color: #333;
  text-align: center;
}

.study-session-card .session-info {
  padding: 10px 15px;
  font-size: 0.9rem;
  color: #666;
  text-align: center;
}

/* Study session page styles */
.study-page {
  max-width: 800px;
  margin: 0 auto;
}

.study-container {
  background: white;
  padding: 30px;
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  min-height: 500px;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.back-link {
  display: inline-block;
  margin-bottom: 20px;
  color: #f44336;
  text-decoration: none;
  font-weight: 500;
}

.back-link:hover {
  text-decoration: underline;
}

/* Problem display */
.problem-container {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 5px;
  padding-bottom: 30px;
  min-height: 400px;
  text-align: center;
  overflow: hidden;
}

.problem-display {
  font-size: 3rem;
  color: #333;
  font-weight: bold;
  margin: 20px 0;
}

/* Stacked problem display */
.stacked-problem {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  font-size: 2.5rem;
  color: #333;
  font-weight: bold;
  margin: 20px 0;
  min-width: 200px;
}

.stacked-numbers {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 5px;
}

.stacked-number {
  display: flex;
  align-items: center;
  gap: 10px;
}

.stacked-operator {
  width: 30px;
  text-align: right;
}

.stacked-operator-spacer {
  width: 30px;
}

.stacked-value {
  min-width: 80px;
  text-align: right;
}

.stacked-line {
  width: 100%;
  height: 2px;
  background: #333;
  margin: 10px 0;
}

.stacked-answer {
  text-align: right;
  min-width: 80px;
}

/* Division stacked display */
.stacked-division {
  align-items: flex-start;
}

.division-container {
  display: flex;
  align-items: flex-start;
  position: relative;
}

.division-divisor {
  margin-top: 3px;
  font-size: 2.5rem;
  font-weight: bold;
  margin-right: 8px;
  min-width: 40px;
  text-align: right;
  line-height: 1.2;
}

.division-bracket-wrapper {
  position: relative;
  display: flex;
  flex-direction: column;
}

.division-bracket-horizontal {
  width: 100%;
  height: 2px;
  background: #333;
  margin-bottom: 2px;
}

.division-bracket-vertical {
  position: absolute;
  left: 0;
  top: 0;
  width: 2px;
  height: 100%;
  background: #333;
}

.division-dividend {
  font-size: 2.5rem;
  font-weight: bold;
  text-align: left;
  padding-left: 8px;
  min-width: 80px;
  position: relative;
  z-index: 1;
}

.division-equals {
  font-size: 2.5rem;
  font-weight: bold;
  align-self: center;
  margin-left: 10px;
}

.problem-answer {
  font-size: 2rem;
  color: #2196f3;
  margin: 20px 0;
}

/* Answer input */
.answer-input {
  font-size: 2rem;
  padding: 15px 20px;
  border: 3px solid #2196f3;
  border-radius: 8px;
  text-align: center;
  width: 200px;
  margin: 20px 0;
}

.answer-input:focus {
  outline: none;
  border-color: #f44336;
  box-shadow: 0 0 10px rgba(244, 67, 54, 0.3);
}

/* Multiple choice options */
.multiple-choice-options {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 15px;
  max-width: 500px;
  margin: 20px auto;
}

.multiple-choice-option {
  padding: 20px;
  font-size: 1.5rem;
  background: white;
  border: 3px solid #2196f3;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
  font-weight: bold;
}

.multiple-choice-option:hover {
  background: #e3f2fd;
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.multiple-choice-option.correct {
  background: #42b983;
  color: white;
  border-color: #42b983;
}

.multiple-choice-option.incorrect {
  background: #f44336;
  color: white;
  border-color: #f44336;
}

/* Navigation */
.navigation {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 20px;
  padding: 20px;
  background: #f9f9f9;
  border-radius: 8px;
  gap: 15px;
  flex-wrap: wrap;
}

.nav-button {
  padding: 12px 24px;
  font-size: 1rem;
  background: #f44336;
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  font-weight: 500;
  transition: background 0.2s;
  flex: 1 1 auto;
  min-width: 100px;
}

.nav-button:hover:not(:disabled) {
  background: #d32f2f;
}

.prev-button {
  background: #9e9e9e;
}

.prev-button:hover:not(:disabled) {
  background: #757575;
}

.next-button {
  background: #42b983;
}

.next-button:hover:not(:disabled) {
  background: #35a372;
}

.submit-button {
  background: #2196f3;
}

.submit-button:hover:not(:disabled) {
  background: #1976d2;
}

.nav-button:disabled {
  background: #ccc;
  cursor: not-allowed;
  opacity: 0.6;
}

.progress-indicator {
  font-size: 1.1rem;
  color: #666;
  font-weight: 500;
  flex: 0 0 auto;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 15px;
}

.streak-counter {
  color: #ff6b6b;
  font-weight: bold;
  font-size: 1rem;
  display: flex;
  align-items: center;
  gap: 5px;
}

.streak-emoji {
  display: inline-block;
  font-size: 1.2rem;
  transition: transform 0.3s ease-out, font-size 0.3s ease-out;
}

.floating-emoji {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 4rem;
  z-index: 10000;
  pointer-events: none;
  animation: floatEmojiUp 1s ease-out forwards;
  --target-x: 0px;
  --target-y: -30vh;
}

@keyframes floatEmojiUp {
  0% {
    transform: translate(-50%, -50%) scale(2);
    font-size: 4rem;
    opacity: 1;
  }
  50% {
    opacity: 1;
  }
  100% {
    transform: translate(calc(-50% + var(--target-x, 0px)), calc(-50% + var(--target-y, -30vh))) scale(0.3);
    font-size: 1.2rem;
    opacity: 0;
  }
}

.answer-indicator {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  font-size: 1.2rem;
  font-weight: bold;
}

.answer-indicator.correct {
  background: #42b983;
  color: white;
}

.answer-indicator.incorrect {
  background: #f44336;
  color: white;
}

.progress-bar {
  display: flex;
  gap: 0;
  justify-content: center;
  flex-wrap: nowrap;
  margin: 15px 0;
  width: 100%;
  padding: 5px 0;
  box-sizing: border-box;
}

.progress-dot {
  flex: 1 1 auto;
  min-width: 4px;
  height: 10px;
  border-radius: 0;
  background: #ccc;
  transition: all 0.2s;
}

.progress-dot.correct {
  background: #42b983;
}

.progress-dot.incorrect {
  background: #f44336;
}

.progress-dot.current {
  transform: scale(1.3);
  box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.3);
}

/* Configuration panel */
.config-panel {
  background: #f9f9f9;
  padding: 20px;
  border-radius: 8px;
  margin-bottom: 20px;
}

.config-section {
  margin-bottom: 20px;
}

.config-section h3 {
  margin-bottom: 10px;
  color: #333;
  font-size: 1.2rem;
}

.config-option {
  margin-bottom: 15px;
}

.config-option-inline {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 15px;
  margin-bottom: 15px;
}

.config-option-inline .config-option {
  margin-bottom: 0;
}

.config-option label {
  display: block;
  margin-bottom: 5px;
  color: #666;
  font-weight: 500;
}

.config-option input,
.config-option select {
  width: 100%;
  padding: 10px;
  border: 2px solid #ddd;
  border-radius: 6px;
  font-size: 1rem;
}

.config-option input:focus,
.config-option select:focus {
  outline: none;
  border-color: #2196f3;
}

.button-group {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.button-group button {
  flex: 1 1 auto;
  min-width: 120px;
}

/* Problem set configuration */
.study-set {
  background: white;
  padding: 15px;
  border-radius: 6px;
  margin-bottom: 15px;
  border: 2px solid #ddd;
}

.number-ranges-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 15px;
  margin-bottom: 15px;
}

.number-range-group {
  padding: 10px;
  background: #f9f9f9;
  border-radius: 6px;
}

.study-set-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}

.study-set-header h4 {
  color: #333;
  font-size: 1.1rem;
}

.remove-set-button {
  padding: 5px 10px;
  background: #f44336;
  color: white;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.9rem;
}

.remove-set-button:hover {
  background: #d32f2f;
}

.operation-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
  margin: 0 auto 15px;
  max-width: 400px;
}

.operation-button {
  aspect-ratio: 1;
  font-size: 2.5rem;
  font-weight: bold;
  background: white;
  border: 3px solid #2196f3;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
  color: #2196f3;
  display: flex;
  align-items: center;
  justify-content: center;
}

.operation-button:hover {
  background: #e3f2fd;
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.operation-button:active {
  transform: translateY(0);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

/* Success/Error messages */
.result-message {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 1000;
  pointer-events: none;
  animation: fadeIn 0.3s;
}

.success-message {
  background: #42b983;
  color: white;
  padding: 20px 40px;
  border-radius: 8px;
  text-align: center;
  font-size: 1.5rem;
  font-weight: bold;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.error-message {
  background: #f44336;
  color: white;
  padding: 20px 40px;
  border-radius: 8px;
  text-align: center;
  font-size: 1.5rem;
  font-weight: bold;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translate(-50%, -50%) scale(0.9);
  }
  to {
    opacity: 1;
    transform: translate(-50%, -50%) scale(1);
  }
}

/* Spark particles for fireworks effect */
.spark-particle {
  position: fixed;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  pointer-events: none;
  z-index: 9999;
  transform: translate(-50%, -50%);
}

.loading, .error {
  text-align: center;
  padding: 40px;
  font-size: 1.2rem;
  color: #666;
}

.error {
  color: #d32f2f;
}

/* Mobile responsive styles */
@media (max-width: 768px) {
  body {
    padding: 10px;
  }

  .study-container {
    padding: 15px;
  }

  .navigation {
    flex-direction: column;
    padding-top: 15px;
  }

  .nav-button {
    width: 100%;
    padding: 14px 20px;
    font-size: 1rem;
  }

  .progress-indicator {
    order: -1;
    width: 100%;
    text-align: center;
    margin-bottom: 5px;
    font-size: 1rem;
  }

  .problem-display {
    font-size: 2rem;
  }

  .answer-input {
    font-size: 1.5rem;
    width: 150px;
  }

  .multiple-choice-options {
    grid-template-columns: 1fr;
  }

  .multiple-choice-option {
    font-size: 1.2rem;
    padding: 15px;
  }

  .operation-grid {
    grid-template-columns: repeat(2, 1fr);
    max-width: 200px;
  }

  .operation-button {
    font-size: 2rem;
  }
}

@media (max-width: 480px) {
  .problem-display {
    font-size: 1.5rem;
  }

  .answer-input {
    font-size: 1.2rem;
    width: 120px;
  }

  .nav-button {
    font-size: 0.95rem;
    padding: 12px 16px;
  }

  .progress-indicator {
    font-size: 0.95rem;
  }
}