:root {
  --bg: #0b0c0f;
  --surface: #11131a;
  --surface-alt: #181b24;
  --border: #262a35;
  --text: #e7e9ee;
  --muted: #9ba2b3;
  --primary: #60a5fa;
  --primary-dark: #3b82f6;
  --accent: #8b5cf6;
  --success: #22c55e;
  --warning: #fbbf24;
  --danger: #ef4444;
}

@media (prefers-color-scheme: light) {
  :root {
    --bg: #f8fafc;
    --surface: #ffffff;
    --surface-alt: #eef2ff;
    --border: #d8dee9;
    --text: #111827;
    --muted: #475569;
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --accent: #7c3aed;
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: radial-gradient(circle at top, rgba(96, 165, 250, 0.08), transparent 55%), var(--bg);
  color: var(--text);
  font: 15px/1.6 "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 32px 18px 48px;
}

.header {
  text-align: center;
  margin-bottom: 32px;
}

.header h1 {
  font-size: clamp(1.8rem, 3vw, 2.4rem);
  margin: 0 0 12px;
  background: linear-gradient(120deg, var(--primary), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.subtitle {
  margin: 0;
  color: var(--muted);
  font-size: 1.05rem;
}

.hint {
  margin-top: 12px;
  color: var(--muted);
  font-size: 0.9rem;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 20px;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 24px;
  box-shadow: 0 25px 45px -30px rgba(15, 23, 42, 0.4);
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.card h2 {
  margin: 0;
  font-size: 1.35rem;
  display: flex;
  align-items: center;
  gap: 10px;
}

.card-desc {
  margin: 0;
  font-size: 0.95rem;
  color: var(--muted);
}

.preset-bar {
  display: flex;
  flex-direction: column;
  gap: 8px;
  background: rgba(96, 165, 250, 0.08);
  border: 1px solid rgba(96, 165, 250, 0.25);
  border-radius: 12px;
  padding: 12px 14px;
}

.preset-bar label span {
  font-weight: 600;
  color: var(--text);
}

#buffer-preset {
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface-alt);
  color: inherit;
  font: inherit;
}

#buffer-preset:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
  border-color: var(--primary);
}

.preset-hint {
  margin: 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.form-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px 16px;
}

label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-weight: 600;
  color: var(--text);
}

input[type="number"] {
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface-alt);
  color: inherit;
  font: inherit;
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

input[type="number"]:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
  border-color: var(--primary);
  box-shadow: 0 0 0 4px rgba(96, 165, 250, 0.25);
}

input.input-invalid {
  border-color: var(--danger) !important;
  box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.2);
}

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

.btn {
  padding: 10px 18px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: transparent;
  color: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease, border-color 0.15s ease;
}

.btn:hover {
  transform: translateY(-1px);
  border-color: var(--primary);
}

.btn.primary {
  background: linear-gradient(120deg, var(--primary), var(--accent));
  color: #fff;
  border-color: transparent;
}

.btn.primary:hover {
  box-shadow: 0 10px 25px -15px rgba(96, 165, 250, 0.8);
}

.btn.copy {
  background: var(--success);
  border-color: var(--success);
  color: #fff;
}

.btn.copy:hover {
  box-shadow: 0 8px 20px -12px rgba(34, 197, 94, 0.75);
}

.btn.ghost {
  border-style: dashed;
  color: var(--muted);
}

.btn.ghost:hover {
  color: var(--text);
}

.result {
  min-height: 40px;
  padding: 14px 16px;
  background: linear-gradient(135deg, rgba(96, 165, 250, 0.12), rgba(139, 92, 246, 0.08));
  border: 1px solid rgba(96, 165, 250, 0.35);
  border-radius: 12px;
  font-weight: 600;
}

.result:empty {
  display: none;
}

.steps {
  font-size: 0.85rem;
  color: var(--muted);
  background: rgba(96, 165, 250, 0.08);
  border-radius: 10px;
  padding: 12px 14px;
  display: none;
  line-height: 1.5;
}

.steps:not(:empty) {
  display: block;
}

.toast {
  position: fixed;
  top: 20px;
  right: 20px;
  background: var(--primary);
  color: #fff;
  padding: 12px 18px;
  border-radius: 12px;
  box-shadow: 0 10px 35px -20px rgba(96, 165, 250, 0.9);
  z-index: 9999;
  opacity: 0.95;
}

.toast.error {
  background: var(--danger);
}

.serial-warning {
  color: var(--warning);
  font-weight: 600;
}

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

@media (max-width: 680px) {
  .container {
    padding: 26px 14px 40px;
  }

  .card {
    padding: 20px;
  }

  .row {
    flex-direction: column;
  }

  .btn {
    width: 100%;
    text-align: center;
  }

  .preset-bar {
    padding: 10px 12px;
  }
}

@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;
  }
}