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

:root {
  --color-bg: #f5f7fa;
  --color-surface: #ffffff;
  --color-primary: #3b82f6;
  --color-primary-hover: #2563eb;
  --color-text: #1e293b;
  --color-text-muted: #64748b;
  --color-border: #e2e8f0;
  --color-error: #ef4444;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.1);
}

/* Dark mode – system preference */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme='light']) {
    --color-bg: #0f172a;
    --color-surface: #1e293b;
    --color-primary: #60a5fa;
    --color-primary-hover: #3b82f6;
    --color-text: #f1f5f9;
    --color-text-muted: #94a3b8;
    --color-border: #334155;
    --color-error: #f87171;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.4);
  }
}

/* Dark mode – manual toggle */
:root[data-theme='dark'] {
  --color-bg: #0f172a;
  --color-surface: #1e293b;
  --color-primary: #60a5fa;
  --color-primary-hover: #3b82f6;
  --color-text: #f1f5f9;
  --color-text-muted: #94a3b8;
  --color-border: #334155;
  --color-error: #f87171;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.4);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen,
    Ubuntu, Cantarell, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
}

.container {
  max-width: 640px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

/* Header */
header {
  text-align: center;
  margin-bottom: 2rem;
}

.header-row {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 0.75rem;
}

header h1 {
  font-size: 1.8rem;
  font-weight: 700;
  margin-bottom: 0.25rem;
}

#theme-toggle {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 50%;
  width: 2.2rem;
  height: 2.2rem;
  font-size: 1.1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.15s, border-color 0.15s;
  flex-shrink: 0;
}

#theme-toggle:hover {
  background: var(--color-bg);
  border-color: var(--color-primary);
}

.subtitle {
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

nav {
  margin-top: 0.75rem;
}

nav a {
  color: var(--color-primary);
  text-decoration: none;
  font-size: 0.875rem;
  font-weight: 500;
}

nav a:hover {
  text-decoration: underline;
}

/* Form */
form {
  background: var(--color-surface);
  padding: 1.5rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  margin-bottom: 1.5rem;
}

.form-group {
  margin-bottom: 1rem;
}

.form-group label {
  display: block;
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: 0.35rem;
  color: var(--color-text-muted);
}

.form-group input,
.form-group select {
  width: 100%;
  padding: 0.6rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: 6px;
  font-size: 0.95rem;
  color: var(--color-text);
  background: var(--color-bg);
  transition: border-color 0.15s;
}

.form-group input:focus,
.form-group select:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.15);
}

.form-row {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
}

.form-row-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.75rem;
}

.type-fields {
  transition: opacity 0.15s;
}

.form-group input[type='checkbox'] {
  width: auto;
  margin-right: 0.4rem;
  vertical-align: middle;
}

@media (max-width: 500px) {
  .form-row,
  .form-row-2 {
    grid-template-columns: 1fr;
  }
}

/* Advanced options panel */
#advanced-options {
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 0;
  margin-bottom: 1rem;
}

#advanced-options summary {
  cursor: pointer;
  font-weight: 600;
  font-size: 0.9rem;
  padding: 0.65rem 0.85rem;
  color: var(--color-text-muted);
  user-select: none;
  list-style: none;
}

#advanced-options summary::-webkit-details-marker { display: none; }

#advanced-options summary::before {
  content: '▸ ';
}

#advanced-options[open] summary::before {
  content: '▾ ';
}

#advanced-options[open] summary {
  border-bottom: 1px solid var(--color-border);
  margin-bottom: 0;
}

.advanced-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
  padding: 0.85rem;
}

@media (max-width: 500px) {
  .advanced-grid {
    grid-template-columns: 1fr;
  }
}

.color-group {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.color-group input[type='color'] {
  width: 36px;
  height: 36px;
  padding: 2px;
  border: 1px solid var(--color-border);
  border-radius: 6px;
  cursor: pointer;
  background: none;
}

.color-group span {
  font-size: 0.82rem;
  font-family: monospace;
  color: var(--color-text-muted);
}

input[type='range'] {
  width: 100%;
  accent-color: var(--color-primary);
}

button[type='submit'] {
  width: 100%;
  padding: 0.7rem;
  background: var(--color-primary);
  color: #fff;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
}

button[type='submit']:hover {
  background: var(--color-primary-hover);
}

button[type='submit']:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

button[type='submit'].dirty {
  background: #f59e0b;
}

button[type='submit'].dirty:hover {
  background: #d97706;
}

/* Preview */
#preview-section {
  background: var(--color-surface);
  padding: 1.5rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  text-align: center;
}

#preview-section h2 {
  font-size: 1rem;
  margin-bottom: 1rem;
  color: var(--color-text-muted);
}

#qr-preview {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 180px;
}

#qr-preview img,
#qr-preview svg {
  max-width: 100%;
  height: auto;
  border-radius: 6px;
}

.actions {
  margin-top: 1rem;
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 0.55rem 1.5rem;
  background: var(--color-primary);
  color: #fff;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
  font-size: 0.9rem;
  transition: background 0.15s;
  border: none;
  cursor: pointer;
}

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

.btn-secondary {
  background: transparent;
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
}

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

/* Transparent preview (checkerboard) */
.transparent-preview {
  background-image:
    repeating-conic-gradient(#ccc 0% 25%, #fff 0% 50%);
  background-size: 16px 16px;
  border-radius: 6px;
  padding: 0.5rem;
}

/* Error */
#error-section {
  background: var(--color-surface);
  padding: 1rem 1.5rem;
  border-radius: var(--radius);
  border-left: 4px solid var(--color-error);
}

#error-message {
  color: var(--color-error);
  font-size: 0.9rem;
}

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

/* Footer */
footer {
  text-align: center;
  margin-top: 2.5rem;
  color: var(--color-text-muted);
  font-size: 0.8rem;
}

footer a {
  color: var(--color-primary);
  text-decoration: none;
}