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

:root {
  /* Backgrounds — warm dark tones */
  --bg-primary: #1e1b2e;
  --bg-secondary: #2a2540;
  --bg-card: #332e4a;
  --bg-input: #1a1730;

  /* Accents — playful & warm */
  --accent: #ff6b6b;
  --accent-secondary: #4ecdc4;
  --accent-purple: #a78bfa;
  --accent-orange: #ffa94d;
  --accent-yellow: #ffe066;
  --accent-pink: #f472b6;

  /* Gradients */
  --gradient-primary: linear-gradient(135deg, #ff6b6b, #ee5a24);
  --gradient-success: linear-gradient(135deg, #4ecdc4, #44bd9e);
  --gradient-warning: linear-gradient(135deg, #ffa94d, #ff8c00);
  --gradient-fun: linear-gradient(135deg, #a78bfa, #f472b6);

  /* Text */
  --text-primary: #f0edf6;
  --text-secondary: #b8b0cc;
  --text-muted: #7a7290;

  /* Borders */
  --border: #3d3659;
  --border-hover: #5a4f80;

  /* Semantic */
  --danger: #ff6b6b;
  --success: #4ecdc4;
  --warning: #ffa94d;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(0,0,0,0.2);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.25);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.3);

  /* Radii */
  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 20px;
  --radius-pill: 50px;

  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-primary);
  background-image:
    radial-gradient(circle at 20% 80%, rgba(167,139,250,0.06) 0%, transparent 50%),
    radial-gradient(circle at 80% 20%, rgba(255,107,107,0.06) 0%, transparent 50%);
  background-attachment: fixed;
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
}

h1, h2, h3, h4, h5, h6,
.card-title, .section-title, .page-title {
  font-family: 'Fredoka', sans-serif;
}

a { color: var(--accent-purple); text-decoration: none; transition: color var(--transition-fast); }
a:hover { color: var(--accent-pink); }

/* Animations */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes bounceIn {
  0% { opacity: 0; transform: scale(0.8); }
  60% { transform: scale(1.05); }
  100% { opacity: 1; transform: scale(1); }
}
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-6px); }
  75% { transform: translateX(6px); }
}
@keyframes pulse {
  0%, 100% { box-shadow: 0 0 8px rgba(167,139,250,0.3); }
  50% { box-shadow: 0 0 16px rgba(167,139,250,0.5); }
}
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

/* Header */
.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 16px 28px;
  background: rgba(42,37,64,0.92);
  backdrop-filter: blur(12px);
  border-bottom: 2px solid var(--border);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 0;
  z-index: 50;
}
.header h1 {
  font-size: 1.5rem;
  font-family: 'Fredoka', sans-serif;
  font-weight: 600;
  letter-spacing: -0.5px;
}
.header h1 span {
  background: var(--gradient-fun);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.header-right { display: flex; align-items: center; gap: 16px; }
.header-user { color: var(--text-secondary); font-size: 0.9rem; }

/* Buttons */
.btn {
  padding: 10px 24px;
  border: none;
  border-radius: var(--radius-pill);
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 600;
  font-family: 'Inter', sans-serif;
  transition: transform var(--transition-fast), box-shadow var(--transition-normal), opacity var(--transition-fast);
  position: relative;
  overflow: hidden;
}
.btn:hover { transform: translateY(-2px) scale(1.02); box-shadow: var(--shadow-md); }
.btn:active { transform: translateY(0) scale(0.98); box-shadow: none; }
.btn-primary { background: var(--gradient-primary); color: #fff; box-shadow: 0 4px 12px rgba(255,107,107,0.3); }
.btn-success { background: var(--gradient-success); color: #fff; box-shadow: 0 4px 12px rgba(78,205,196,0.3); }
.btn-warning { background: var(--gradient-warning); color: #fff; box-shadow: 0 4px 12px rgba(255,169,77,0.3); }
.btn-outline {
  background: transparent;
  border: 2px solid var(--border);
  color: var(--text-secondary);
  border-radius: var(--radius-pill);
}
.btn-outline:hover { border-color: var(--accent-purple); color: var(--accent-purple); background: rgba(167,139,250,0.08); }
.btn-sm { padding: 7px 16px; font-size: 0.8rem; }
.btn:disabled { opacity: 0.4; cursor: not-allowed; transform: none !important; box-shadow: none !important; }

/* Auth page */
.auth-container {
  max-width: 420px;
  margin: 60px auto;
  padding: 40px 36px;
  background: rgba(42,37,64,0.7);
  backdrop-filter: blur(12px);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
  animation: fadeInUp 0.5s ease-out;
}
.auth-container::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: var(--gradient-fun);
}
.auth-container h2 { text-align: center; margin-bottom: 28px; font-family: 'Fredoka', sans-serif; font-size: 1.8rem; }
.auth-container h2 span {
  background: var(--gradient-fun);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.form-group { margin-bottom: 18px; }
.form-group label { display: block; margin-bottom: 8px; font-size: 0.88rem; font-weight: 500; color: var(--text-secondary); }
.form-group input, .form-group select {
  width: 100%;
  padding: 12px 16px;
  background: var(--bg-input);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.95rem;
  font-family: 'Inter', sans-serif;
  transition: border-color var(--transition-normal), box-shadow var(--transition-normal);
}
.form-group input:focus, .form-group select:focus {
  outline: none;
  border-color: var(--accent-purple);
  box-shadow: 0 0 0 3px rgba(167,139,250,0.2);
}
.form-group input::placeholder { color: var(--text-muted); opacity: 0.6; }

.form-error { color: var(--danger); font-size: 0.85rem; margin-top: 8px; text-align: center; animation: shake 0.3s ease; }
.form-toggle { text-align: center; margin-top: 20px; font-size: 0.88rem; color: var(--text-secondary); }
.form-toggle span[style*="cursor"] { color: var(--accent-purple) !important; font-weight: 600; }
.form-toggle span[style*="cursor"]:hover { color: var(--accent-pink) !important; }

/* Main content */
.main { padding: 24px; max-width: 1200px; margin: 0 auto; animation: fadeInUp 0.4s ease-out; }
.page-title { font-size: 1.3rem; margin-bottom: 20px; }

/* Tabs */
.tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 28px;
  border-bottom: 2px solid var(--border);
}
.tab {
  padding: 12px 24px;
  cursor: pointer;
  color: var(--text-muted);
  border-bottom: 3px solid transparent;
  transition: color var(--transition-normal), border-color var(--transition-normal), background var(--transition-normal);
  font-size: 0.92rem;
  font-weight: 600;
  font-family: 'Fredoka', sans-serif;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0;
  margin-bottom: -2px;
}
.tab:hover { color: var(--text-primary); background: rgba(167,139,250,0.06); }
.tab.active { color: var(--accent-purple); border-bottom-color: var(--accent-purple); background: rgba(167,139,250,0.08); }
.tab-content { display: none; }
.tab-content.active { display: block; animation: fadeInUp 0.3s ease-out; }

/* Cards */
.card {
  background: rgba(42,37,64,0.6);
  backdrop-filter: blur(8px);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 24px;
  margin-bottom: 16px;
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition-normal), transform var(--transition-normal);
}
.card:hover { box-shadow: var(--shadow-md); }
.card-title { font-size: 1.1rem; font-weight: 600; margin-bottom: 10px; font-family: 'Fredoka', sans-serif; }
.card-meta { font-size: 0.8rem; color: var(--text-secondary); margin-bottom: 12px; }

/* Worksheet cards */
.worksheet-card {
  background: rgba(42,37,64,0.6);
  backdrop-filter: blur(8px);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 22px;
  cursor: pointer;
  transition: border-color var(--transition-normal), transform var(--transition-normal), box-shadow var(--transition-normal);
  position: relative;
  overflow: hidden;
}
.worksheet-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--gradient-fun);
  border-radius: var(--radius-md) var(--radius-md) 0 0;
}
.worksheet-card:hover { border-color: var(--accent-purple); transform: translateY(-4px); box-shadow: var(--shadow-lg); }
.worksheet-card.backlog { border-left: 4px solid var(--warning); }
.worksheet-card.backlog::before { background: var(--gradient-warning); }
.worksheet-card h3 { font-size: 1.05rem; margin-bottom: 8px; font-family: 'Fredoka', sans-serif; }
.worksheet-card .meta { font-size: 0.82rem; color: var(--text-secondary); margin-bottom: 12px; }
.worksheet-card .meta .backlog-badge {
  background: var(--gradient-warning);
  color: #fff;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  font-size: 0.7rem;
  font-weight: 700;
  margin-left: 8px;
  letter-spacing: 0.5px;
}

/* Progress bar */
.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--bg-input);
  border-radius: var(--radius-pill);
  overflow: hidden;
}
.progress-bar .fill {
  height: 100%;
  border-radius: var(--radius-pill);
  transition: width 0.5s cubic-bezier(0.4,0,0.2,1);
}
.progress-bar .fill.green { background: var(--gradient-success); }
.progress-bar .fill.red { background: var(--gradient-primary); }
.progress-text { font-size: 0.82rem; color: var(--text-secondary); margin-top: 6px; }

/* Worksheet grid */
.worksheet-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
  margin-bottom: 24px;
}

/* Solver */
.solver-container {
  max-width: 700px;
  margin: 0 auto;
  text-align: center;
  animation: fadeInUp 0.4s ease-out;
}
.solver-header { margin-bottom: 32px; }
.solver-header h2 { font-size: 1.4rem; margin-bottom: 10px; font-family: 'Fredoka', sans-serif; }

.question-display {
  background: rgba(42,37,64,0.7);
  backdrop-filter: blur(8px);
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 44px 40px;
  margin-bottom: 24px;
  box-shadow: var(--shadow-md);
  position: relative;
  overflow: hidden;
}
/* Notebook lines */
.question-display::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: repeating-linear-gradient(180deg, transparent, transparent 38px, rgba(167,139,250,0.04) 38px, rgba(167,139,250,0.04) 40px);
  pointer-events: none;
}
/* Notebook margin line */
.question-display::after {
  content: '';
  position: absolute;
  top: 0; bottom: 0; left: 60px;
  width: 2px;
  background: rgba(255,107,107,0.1);
  pointer-events: none;
}
.question-number { font-size: 0.92rem; color: var(--text-muted); margin-bottom: 20px; font-family: 'Fredoka', sans-serif; }

/* Stacked question layout */
.question-stacked {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-end;
  margin-bottom: 24px;
  font-size: 2.8rem;
  font-weight: 700;
  font-family: 'JetBrains Mono', monospace;
  letter-spacing: 4px;
  position: relative;
  z-index: 1;
}
.stacked-row {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  width: 100%;
}
.stacked-sign {
  color: var(--accent-purple);
  width: 1.2em;
  text-align: center;
  flex-shrink: 0;
  font-weight: 700;
}
.stacked-number {
  text-align: right;
  min-width: 2em;
}
.stacked-line {
  width: 50%;
  height: 4px;
  background: var(--gradient-fun);
  border-radius: 2px;
  margin-top: 10px;
  margin-left: auto;
}

/* Answer input row */
.answer-row-inline {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
  margin-top: 20px;
  position: relative;
  z-index: 1;
}
.stacked-input {
  background: var(--bg-input);
  border: 3px solid var(--accent-purple);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 2.5rem;
  font-weight: 700;
  font-family: 'JetBrains Mono', monospace;
  letter-spacing: 4px;
  text-align: center;
  width: 180px;
  padding: 10px 0;
  outline: none;
  -moz-appearance: textfield;
  transition: border-color var(--transition-normal), box-shadow var(--transition-normal);
}
.stacked-input::placeholder { color: var(--text-muted); opacity: 0.3; }
.stacked-input:focus {
  border-color: var(--accent-pink);
  box-shadow: 0 0 0 4px rgba(244,114,182,0.2), 0 0 20px rgba(244,114,182,0.1);
}

/* Answered display */
.stacked-answer-display {
  margin: 16px auto 0;
  font-size: 2.5rem;
  font-weight: 700;
  font-family: 'JetBrains Mono', monospace;
  letter-spacing: 4px;
  text-align: center;
  width: 50%;
  padding: 8px 0;
  position: relative;
  z-index: 1;
}
.answer-correct { color: var(--success); animation: bounceIn 0.3s ease; }
.answer-wrong { color: var(--danger); animation: shake 0.3s ease; }

/* Feedback */
.feedback {
  padding: 18px;
  border-radius: var(--radius-sm);
  margin-top: 18px;
  font-size: 1.15rem;
  font-weight: 600;
  font-family: 'Fredoka', sans-serif;
  display: none;
  position: relative;
  z-index: 1;
}
.feedback.correct {
  display: block;
  background: rgba(78,205,196,0.12);
  border: 2px solid var(--success);
  color: var(--success);
  animation: bounceIn 0.4s cubic-bezier(0.175,0.885,0.32,1.275);
}
.feedback.wrong {
  display: block;
  background: rgba(255,107,107,0.12);
  border: 2px solid var(--danger);
  color: var(--danger);
  animation: shake 0.4s ease;
}

/* Progress dots */
.progress-dots {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin-bottom: 28px;
}
.progress-dot {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 700;
  border: 2px solid var(--border);
  color: var(--text-muted);
  cursor: pointer;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), background var(--transition-normal), border-color var(--transition-normal);
  font-family: 'Fredoka', sans-serif;
}
.progress-dot:hover { transform: scale(1.2); box-shadow: var(--shadow-sm); }
.progress-dot.current {
  border-color: var(--accent-purple);
  color: var(--accent-purple);
  box-shadow: 0 0 12px rgba(167,139,250,0.3);
  animation: pulse 1.5s ease infinite;
}
.progress-dot.correct {
  background: var(--gradient-success);
  border-color: transparent;
  color: #fff;
  box-shadow: 0 2px 8px rgba(78,205,196,0.3);
}
.progress-dot.wrong {
  background: var(--gradient-primary);
  border-color: transparent;
  color: #fff;
  box-shadow: 0 2px 8px rgba(255,107,107,0.3);
}

/* Summary */
.summary {
  background: rgba(42,37,64,0.7);
  backdrop-filter: blur(8px);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 48px;
  text-align: center;
  box-shadow: var(--shadow-lg);
  animation: fadeInUp 0.5s ease-out;
}
.summary h2 { margin-bottom: 20px; font-family: 'Fredoka', sans-serif; font-size: 1.6rem; }
.summary .score { font-size: 3.5rem; font-weight: 700; margin-bottom: 8px; font-family: 'Fredoka', sans-serif; }
.summary .score.good {
  background: var(--gradient-success);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.summary .score.ok {
  background: var(--gradient-warning);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.summary .score.bad { color: var(--danger); }

/* Stats grid */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 14px;
  margin-bottom: 28px;
}
.stat-card {
  background: rgba(42,37,64,0.6);
  backdrop-filter: blur(8px);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 20px;
  text-align: center;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}
.stat-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); }
.stat-value { font-size: 2rem; font-weight: 700; font-family: 'Fredoka', sans-serif; color: var(--accent-purple); }
.stat-label { font-size: 0.82rem; color: var(--text-secondary); margin-top: 6px; font-weight: 500; }

/* Tables */
.data-table { width: 100%; border-collapse: collapse; margin-top: 14px; }
.data-table th, .data-table td {
  padding: 12px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
  font-size: 0.88rem;
}
.data-table th {
  color: var(--text-muted);
  font-weight: 600;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}
.data-table tr { transition: background var(--transition-fast); }
.data-table tr:hover { background: rgba(167,139,250,0.06); }
.data-table tbody tr:last-child td { border-bottom: none; }

/* Weakness bars */
.weakness-bar-container { margin-bottom: 14px; }
.weakness-bar-label { display: flex; justify-content: space-between; font-size: 0.88rem; margin-bottom: 6px; }
.weakness-bar {
  width: 100%;
  height: 12px;
  background: var(--bg-input);
  border-radius: var(--radius-pill);
  overflow: hidden;
}
.weakness-bar .fill {
  height: 100%;
  border-radius: var(--radius-pill);
  transition: width 0.6s cubic-bezier(0.4,0,0.2,1);
}

/* Form layout */
.form-row { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }

/* Section headers */
.section-title {
  font-size: 1.1rem;
  font-weight: 600;
  font-family: 'Fredoka', sans-serif;
  margin-bottom: 18px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--border);
}

/* Checkbox list */
.checkbox-list { display: flex; flex-wrap: wrap; gap: 10px; }
.checkbox-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  background: var(--bg-input);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.88rem;
  transition: border-color var(--transition-normal), background var(--transition-normal);
}
.checkbox-item:hover { border-color: var(--accent-purple); background: rgba(167,139,250,0.06); }
.checkbox-item input[type="checkbox"] { accent-color: var(--accent-purple); width: 16px; height: 16px; }

/* Messages */
.message {
  padding: 14px 18px;
  border-radius: var(--radius-sm);
  margin-bottom: 16px;
  font-size: 0.9rem;
  font-weight: 500;
  animation: fadeInUp 0.3s ease-out;
}
.message-success { background: rgba(78,205,196,0.12); border: 1px solid var(--success); color: var(--success); }
.message-error { background: rgba(255,107,107,0.12); border: 1px solid var(--danger); color: var(--danger); }
.message-info { background: rgba(167,139,250,0.1); border: 1px solid var(--accent-purple); color: var(--text-secondary); }

/* Empty state */
.empty-state { text-align: center; padding: 48px; color: var(--text-muted); }
.empty-state p { margin-top: 8px; font-size: 0.95rem; font-family: 'Fredoka', sans-serif; }

/* Modal */
.modal-overlay {
  position: fixed; top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0,0,0,0.6);
  backdrop-filter: blur(4px);
  display: flex; align-items: center; justify-content: center;
  z-index: 100;
  animation: fadeIn 0.2s ease;
}
.modal {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  max-width: 520px;
  width: 90%;
  max-height: 80vh;
  overflow-y: auto;
  box-shadow: var(--shadow-lg);
  animation: fadeInUp 0.3s ease-out;
}
.modal h3 { margin-bottom: 18px; font-family: 'Fredoka', sans-serif; }
.modal-actions { display: flex; gap: 10px; justify-content: flex-end; margin-top: 20px; }

/* Scrollbar */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: var(--bg-primary); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--border-hover); }

/* Responsive */
@media (max-width: 600px) {
  .form-row { grid-template-columns: 1fr; }
  .header { flex-direction: column; gap: 10px; text-align: center; padding: 14px 16px; }
  .question-stacked { font-size: 2rem; }
  .stacked-input { font-size: 2rem; width: 150px; }
  .stacked-answer-display { font-size: 2rem; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .auth-container { margin: 30px 16px; padding: 28px 20px; }
  .solver-container { padding: 0 8px; }
  .question-display { padding: 28px 20px; }
  .question-display::after { display: none; }
  .progress-dot { width: 28px; height: 28px; font-size: 0.7rem; }
  .btn { padding: 10px 20px; }
  .btn-sm { padding: 8px 14px; }
  .tabs { overflow-x: auto; }
  .tab { padding: 10px 16px; white-space: nowrap; font-size: 0.85rem; }
}

@media (pointer: coarse) {
  .btn { min-height: 44px; }
  .btn-sm { min-height: 36px; }
  .tab { min-height: 44px; }
  .progress-dot { min-width: 36px; min-height: 36px; }
  .checkbox-item { min-height: 44px; }
}