:root {
  --bg: #f5f7fb;
  --surface: #ffffff;
  --text: #1f2937;
  --subtext: #4b5563;
  --border: #e5e7eb;
  --input-border: #d1d5db;
  --button-bg: #2563eb;
  --button-bg-hover: #1d4ed8;
  --result-bg: #f9fafb;
  --error: #b91c1c;
  color-scheme: light;
}

html[data-theme="dark"] {
  --bg: #0f172a;
  --surface: #1e293b;
  --text: #e5e7eb;
  --subtext: #cbd5e1;
  --border: #334155;
  --input-border: #475569;
  --button-bg: #3b82f6;
  --button-bg-hover: #2563eb;
  --result-bg: #111827;
  --error: #fca5a5;
  color-scheme: dark;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Noto Sans KR", sans-serif;
  background: var(--bg);
  color: var(--text);
}

.container {
  max-width: 640px;
  margin: 48px auto;
  padding: 24px;
  background: var(--surface);
  border-radius: 16px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.15);
  border: 1px solid var(--border);
}

.header-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

h1, h2 { margin-top: 0; }

.description { margin-bottom: 20px; color: var(--subtext); }

.controls {
  display: flex;
  gap: 10px;
  align-items: center;
  margin-bottom: 20px;
  flex-wrap: wrap;
}

input[type="number"] {
  width: 120px;
  padding: 8px 10px;
  border: 1px solid var(--input-border);
  border-radius: 8px;
  font-size: 1rem;
  background: var(--surface);
  color: var(--text);
}

button {
  border: none;
  background: var(--button-bg);
  color: #ffffff;
  padding: 10px 16px;
  border-radius: 8px;
  font-size: 0.95rem;
  cursor: pointer;
}

button:hover { background: var(--button-bg-hover); }

.theme-toggle {
  white-space: nowrap;
  background: transparent;
  border: 1px solid var(--input-border);
  color: var(--text);
}

.theme-toggle:hover {
  background: var(--result-bg);
}

.result-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 10px;
}

.result-list li {
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--result-bg);
}

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