/* ===================================================================
   Math Test Generator — Stylesheet
   Mobile-first, clean, modern design with dark mode support
   =================================================================== */

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

:root {
  --color-primary: #2563eb;
  --color-primary-hover: #1d4ed8;
  --color-primary-light: #dbeafe;
  --color-primary-subtle: #eff6ff;
  --color-success: #16a34a;
  --color-success-bg: #f0fdf4;
  --color-success-border: #bbf7d0;
  --color-error: #dc2626;
  --color-error-bg: #fef2f2;
  --color-error-border: #fecaca;
  --color-warning: #d97706;

  --color-bg: #f1f5f9;
  --color-surface: #ffffff;
  --color-text: #0f172a;
  --color-text-secondary: #475569;
  --color-text-muted: #94a3b8;
  --color-border: #e2e8f0;
  --color-border-focus: #93c5fd;
  --color-input-bg: #ffffff;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;

  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
  --font-mono: "SF Mono", SFMono-Regular, ui-monospace, Menlo, Consolas,
    "Liberation Mono", monospace;

  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
}

/* --- Dark mode --- */
@media (prefers-color-scheme: dark) {
  :root {
    --color-primary: #3b82f6;
    --color-primary-hover: #60a5fa;
    --color-primary-light: #1e3a5f;
    --color-primary-subtle: #172554;
    --color-success: #22c55e;
    --color-success-bg: #052e16;
    --color-success-border: #166534;
    --color-error: #ef4444;
    --color-error-bg: #450a0a;
    --color-error-border: #7f1d1d;
    --color-warning: #f59e0b;

    --color-bg: #0f172a;
    --color-surface: #1e293b;
    --color-text: #f1f5f9;
    --color-text-secondary: #94a3b8;
    --color-text-muted: #64748b;
    --color-border: #334155;
    --color-border-focus: #3b82f6;
    --color-input-bg: #0f172a;

    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
  }
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-stack);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* --- Layout --- */
.container {
  width: 100%;
  max-width: 640px;
  margin: 0 auto;
  padding: 16px;
}

/* --- Header --- */
.header {
  text-align: center;
  padding: 24px 0 8px;
}

.header__title {
  font-size: 1.625rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

.header__subtitle {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin-top: 4px;
}

/* --- Card --- */
.card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  padding: 20px;
  margin-bottom: 20px;
}

.card__heading {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 16px;
  color: var(--color-text);
}

/* --- Form --- */
.form-group {
  margin-bottom: 16px;
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  margin-bottom: 6px;
}

.form-group input:not([type="radio"]),
.form-group select {
  width: 100%;
  padding: 12px 14px;
  font-size: 1rem;
  font-family: var(--font-stack);
  color: var(--color-text);
  background-color: var(--color-input-bg);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-sm);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
  appearance: none;
  -webkit-appearance: none;
}

.form-group select {
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 40px;
}

.form-group input:focus,
.form-group select:focus {
  outline: 2px solid var(--color-border-focus);
  outline-offset: -1px;
  border-color: var(--color-border-focus);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.15);
}

.form-group input.is-invalid {
  border-color: var(--color-error);
}

.form-group input.is-invalid:focus {
  outline-color: var(--color-error);
  border-color: var(--color-error);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-error) 15%, transparent);
}

.form-group input.is-valid {
  border-color: var(--color-success);
}

.form-hint {
  font-size: 0.78rem;
  color: var(--color-text-muted);
  margin-top: 5px;
  line-height: 1.4;
}

.form-hint code {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  background: var(--color-primary-subtle);
  color: var(--color-primary);
  padding: 1px 5px;
  border-radius: 3px;
}

.form-feedback {
  font-size: 0.8rem;
  margin-top: 5px;
  min-height: 1.2em;
  line-height: 1.4;
}

.form-feedback.is-error {
  color: var(--color-error);
}

.form-feedback.is-success {
  color: var(--color-success);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

/* --- Advanced Options Toggle --- */
.advanced-toggle {
  margin-bottom: 12px;
}

.advanced-toggle__btn {
  display: flex;
  align-items: center;
  gap: 8px;
  background: none;
  border: none;
  color: var(--color-text-secondary);
  font-size: 0.875rem;
  font-weight: 500;
  font-family: var(--font-stack);
  cursor: pointer;
  padding: 6px 0;
  transition: color var(--transition-fast);
}

.advanced-toggle__btn:hover {
  color: var(--color-primary);
}

.advanced-toggle__icon {
  display: inline-block;
  font-size: 0.65rem;
  transition: transform var(--transition-normal);
}

.advanced-toggle__btn[aria-expanded="true"] .advanced-toggle__icon {
  transform: rotate(90deg);
}

.advanced-options {
  overflow: hidden;
  padding-bottom: 4px;
}

.advanced-options[hidden] {
  display: none;
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: none;
  border-radius: var(--radius-md);
  font-family: var(--font-stack);
  font-weight: 600;
  cursor: pointer;
  transition: background-color var(--transition-fast),
    transform var(--transition-fast), box-shadow var(--transition-fast);
}

.btn:active {
  transform: scale(0.98);
}

.btn--generate {
  width: 100%;
  padding: 16px;
  font-size: 1.075rem;
  color: #ffffff;
  background-color: var(--color-primary);
  box-shadow: var(--shadow-sm);
  margin-top: 4px;
}

.btn--generate:hover {
  background-color: var(--color-primary-hover);
  box-shadow: var(--shadow-md);
}

.btn--generate:disabled {
  opacity: 0.65;
  cursor: not-allowed;
  transform: none;
}

.btn__label,
.btn__spinner {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.btn__label[hidden],
.btn__spinner[hidden] {
  display: none;
}

.btn--secondary {
  padding: 10px 20px;
  font-size: 0.875rem;
  color: var(--color-primary);
  background-color: var(--color-primary-subtle);
  border: 1.5px solid var(--color-border);
}

.btn--secondary:hover {
  background-color: var(--color-primary-light);
}

.btn--show-more {
  width: 100%;
  margin-top: 12px;
}

.btn--show-more[hidden] {
  display: none;
}

/* --- Spinner --- */
.spinner {
  display: inline-block;
  width: 18px;
  height: 18px;
  border: 2.5px solid rgba(255, 255, 255, 0.3);
  border-top-color: #ffffff;
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

/* --- Status / Toast Area --- */
.status-area {
  margin-top: 16px;
}

.status-area[hidden] {
  display: none;
}

.status {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 14px 16px;
  border-radius: var(--radius-md);
  border: 1.5px solid;
  animation: slideIn 0.3s ease;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.status[hidden] {
  display: none;
}

.status--success {
  background-color: var(--color-success-bg);
  border-color: var(--color-success-border);
  color: var(--color-success);
}

.status--error {
  background-color: var(--color-error-bg);
  border-color: var(--color-error-border);
  color: var(--color-error);
}

.status__icon {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  font-size: 0.8rem;
  font-weight: 700;
}

.status--success .status__icon {
  background-color: var(--color-success);
  color: #ffffff;
}

.status--error .status__icon {
  background-color: var(--color-error);
  color: #ffffff;
}

.status__body {
  flex: 1;
  min-width: 0;
}

.status__message {
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 2px;
}

.status__link {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-primary);
  text-decoration: none;
}

.status__link:hover {
  text-decoration: underline;
}

.status__dismiss {
  flex-shrink: 0;
  background: none;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
  color: inherit;
  opacity: 0.5;
  padding: 0 2px;
  line-height: 1;
  transition: opacity var(--transition-fast);
}

.status__dismiss:hover {
  opacity: 1;
}

/* --- Action Bar --- */
.action-bar {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-bottom: 20px;
  flex-wrap: wrap;
}

.btn--action {
  padding: 8px 16px;
  font-size: 0.8rem;
  font-family: var(--font-stack);
  font-weight: 600;
  border: 1.5px solid;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background-color var(--transition-fast), border-color var(--transition-fast),
    transform var(--transition-fast);
}

.btn--action:active {
  transform: scale(0.98);
}

.btn--action:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

.btn--danger {
  color: var(--color-error);
  background-color: var(--color-error-bg);
  border-color: var(--color-error-border);
}

.btn--danger:hover:not(:disabled) {
  background-color: var(--color-error-border);
}

.btn--action:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* --- History --- */
.history-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.history-empty {
  text-align: center;
  color: var(--color-text-muted);
  font-size: 0.9rem;
  padding: 20px 0;
}

.history-empty[hidden] {
  display: none;
}

.history-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  background-color: var(--color-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.history-item:hover {
  border-color: var(--color-border-focus);
  box-shadow: var(--shadow-sm);
}

.history-item__info {
  flex: 1;
  min-width: 0;
}

.history-item__title {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--color-text);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.history-item__title a {
  color: inherit;
  text-decoration: none;
}

.history-item__title a:hover {
  color: var(--color-primary);
  text-decoration: underline;
}

.history-item__time {
  font-size: 0.78rem;
  color: var(--color-text-muted);
  margin-top: 2px;
}

.history-item__actions {
  flex-shrink: 0;
}

.btn--repeat {
  padding: 6px 14px;
  font-size: 0.78rem;
  color: var(--color-primary);
  background: var(--color-primary-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-stack);
  font-weight: 600;
  cursor: pointer;
  transition: background-color var(--transition-fast), border-color var(--transition-fast);
}

.btn--repeat:hover {
  background-color: var(--color-primary-light);
  border-color: var(--color-primary);
}

.btn--generate:focus-visible,
.btn--repeat:focus-visible,
.advanced-toggle__btn:focus-visible,
.status__dismiss:focus-visible,
.btn--secondary:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* --- Missing-file indicator --- */
.history-item__missing {
  color: var(--color-warning);
  margin-right: 6px;
  font-size: 0.85rem;
  cursor: help;
}

.history-item--missing .history-item__title a {
  text-decoration: line-through;
  color: var(--color-text-muted);
}

/* --- Footer --- */
.footer {
  text-align: center;
  font-size: 0.78rem;
  color: var(--color-text-muted);
  padding: 16px 0 24px;
}

/* --- Responsive: Tablet+ --- */
@media (min-width: 480px) {
  .container {
    padding: 24px;
  }

  .header__title {
    font-size: 1.875rem;
  }

  .card {
    padding: 24px;
  }
}

@media (min-width: 640px) {
  .container {
    padding: 32px;
  }

  .header {
    padding: 32px 0 12px;
  }

  .header__title {
    font-size: 2rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}