/* 1. Reset */
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* 2. Base */
body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  background-color: var(--bg-main);
  color: var(--text-main);
  line-height: 1.5;
  transition: background-color var(--transition-speed), color var(--transition-speed);
  padding: var(--spacing-lg);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

@media (min-width: 1024px) {
  body {
    padding: var(--spacing-2xl);
  }
}

a {
  color: var(--accent-colour);
  text-decoration: none;
  transition: opacity var(--transition-speed);
}

a:hover {
  opacity: 0.8;
}

h1, h2, h3 {
  color: var(--primary-colour);
  letter-spacing: -0.025em;
}

h1 {
  font-size: 1.5rem;
  font-weight: 800;
}

@media (min-width: 768px) {
  h1 {
    font-size: 1.875rem;
  }
}

h2 {
  font-size: 1.5rem;
  font-weight: 800;
  margin-bottom: var(--spacing-md);
}

h3 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
}

/* 3. Container */
.container {
  max-width: var(--container-max-width);
  width: 100%;
  margin: 0 auto;
  flex: 1;
}

/* 4. Header */
header {
  margin-bottom: var(--spacing-2xl);
}

.header-top {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.header-brand {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.logo {
  width: 2rem;
  height: 2rem;
  object-fit: contain;
}

@media (min-width: 768px) {
  .logo {
    width: 2.5rem;
    height: 2.5rem;
  }
}

.header-actions {
  display: flex;
  gap: var(--spacing-sm);
}

.header-btn, .theme-toggle {
  background: none;
  border: 2px solid var(--border-colour);
  border-radius: var(--border-radius-md);
  padding: var(--spacing-sm);
  color: var(--text-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all var(--transition-speed);
  width: 2.5rem;
  height: 2.5rem;
}

.header-btn:hover, .theme-toggle:hover {
  background-color: var(--bg-subtle);
  color: var(--primary-colour);
  border-color: var(--accent-colour);
}

.header-accent {
  height: 0.25rem;
  width: 5rem;
  background-color: var(--accent-colour);
  margin-top: var(--spacing-md);
}

/* Theme toggle icon logic */
.theme-toggle .moon-icon { display: none; }
.theme-toggle .sun-icon { display: block; }

[data-theme="dark"] .theme-toggle .sun-icon { display: none; }
[data-theme="dark"] .theme-toggle .moon-icon { display: block; }

/* 5. Main Content / App Layout */
.app-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-xl);
}

@media (min-width: 1024px) {
  .app-grid {
    grid-template-columns: 1fr 1fr;
  }
}

.card {
  background-color: var(--bg-subtle);
  padding: var(--spacing-xl);
  border-radius: var(--border-radius-lg);
  box-shadow: var(--shadow-sm);
}

.form-group {
  margin-bottom: var(--spacing-lg);
}

.form-label {
  display: block;
  font-size: 0.875rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: var(--spacing-sm);
}

.input-row {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-sm);
}

.input-number {
  width: 5rem;
  padding: 0.5rem;
  border: 1px solid var(--border-colour);
  border-radius: var(--border-radius-md);
  background-color: var(--bg-input);
  color: var(--text-main);
  font-weight: 600;
  text-align: center;
}

input[type="range"] {
  flex: 1;
  height: 0.375rem;
  background: var(--bg-range);
  border-radius: var(--border-radius-lg);
  appearance: none;
  accent-color: var(--accent-colour);
}

.checkbox-group {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-lg);
}

.checkbox-item {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  cursor: pointer;
  font-size: 0.9375rem;
  font-weight: 500;
}

.checkbox-item input[type="checkbox"] {
  width: 1.125rem;
  height: 1.125rem;
  accent-color: var(--accent-colour);
  cursor: pointer;
}

.presets-row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-lg);
}

.btn-preset {
  background-color: var(--bg-main);
  border: 1px solid var(--border-colour);
  border-radius: var(--border-radius-sm);
  padding: 0.25rem 0.75rem;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-muted);
  cursor: pointer;
  transition: all var(--transition-speed);
}

.btn-preset:hover {
  border-color: var(--accent-colour);
  color: var(--accent-colour);
}

.btn-preset.active {
  background-color: var(--accent-colour);
  border-color: var(--accent-colour);
  color: #ffffff;
}

.action-row {
  margin-top: var(--spacing-xl);
}

.btn-primary {
  width: 100%;
  background-color: var(--btn-primary-bg);
  color: var(--btn-primary-text);
  border: none;
  border-radius: var(--border-radius-md);
  padding: 0.75rem 1.5rem;
  font-size: 1rem;
  font-weight: 700;
  cursor: pointer;
  transition: opacity var(--transition-speed);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
}

.btn-primary:hover {
  opacity: 0.9;
}

/* Result Section */
.result-container {
  margin-top: var(--spacing-xl);
  background-color: var(--bg-main);
  border-radius: var(--border-radius-md);
  border: 2px solid var(--border-colour);
  overflow: hidden;
}

.result-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--spacing-sm) var(--spacing-md);
  background-color: var(--bg-subtle);
  border-bottom: 1px solid var(--border-colour);
}

.result-label {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--text-muted);
}

.btn-copy {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
  font-size: 0.75rem;
  font-weight: 600;
  transition: color var(--transition-speed);
}

.btn-copy:hover {
  color: var(--accent-colour);
}

.result-display {
  padding: var(--spacing-md);
  font-family: var(--font-mono);
  font-size: 1.125rem;
  word-break: break-all;
  min-height: 3rem;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--primary-colour);
}

.number-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  justify-content: center;
  list-style: none;
  width: 100%;
}

.number-item {
  background-color: var(--bg-subtle);
  padding: 0.25rem 0.75rem;
  border-radius: var(--border-radius-sm);
  border: 1px solid var(--border-colour);
  font-weight: 600;
}

/* 6. Footer */
footer {
  margin-top: 4rem;
  padding-top: var(--spacing-xl);
  border-top: 1px solid var(--border-colour);
  text-align: center;
  color: var(--text-secondary);
  font-size: 0.75rem;
  font-weight: 500;
}

/* 7. Utilities */
.hidden { display: none !important; }

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* 8. Toast Notifications */
#toast-container {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  z-index: 1000;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.toast {
  padding: 1rem 1.5rem;
  background-color: var(--bg-subtle);
  color: var(--text-main);
  border-radius: var(--border-radius-md);
  box-shadow: var(--shadow-md);
  border-left: 4px solid var(--accent-colour);
  min-width: 250px;
  animation: slideIn 0.3s ease-out;
}

.toast.success { border-left-color: var(--success-colour); }
.toast.error   { border-left-color: var(--error-colour); }

.toast-fade-out {
  opacity: 0;
  transform: translateX(1rem);
  transition: opacity 0.3s, transform 0.3s;
}

@keyframes slideIn {
  from { transform: translateX(100%); opacity: 0; }
  to   { transform: translateX(0);    opacity: 1; }
}

/* 9. Print Styles */
@media print {
  .header-actions, .action-row, footer, .presets-row {
    display: none !important;
  }
  body {
    padding: 0;
    background: white;
  }
  .card {
    box-shadow: none;
    border: 1px solid #eee;
  }
}