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

/* ── 라이트 모드 (기본) ── */
:root {
  --bg: #f0f4ff;
  --surface: #ffffff;
  --text: #333333;
  --text-muted: #888888;
  --id-bg: #f0f4ff;
  --id-color: #4a90e2;
  --tag-bg: #f0f4ff;
  --tag-border: #d0d8f0;
  --tag-color: #4a90e2;
  --tag-hover: #d8e4ff;
  --copy-bg: #eeeeee;
  --copy-hover: #dddddd;
  --select-border: #cccccc;
  --footer-bg: #333333;
  --footer-text: #aaaaaa;
  --shadow: rgba(0, 0, 0, 0.1);
}

/* ── 다크 모드 ── */
body.dark {
  --bg: #1a1a2e;
  --surface: #16213e;
  --text: #e0e0e0;
  --text-muted: #888888;
  --id-bg: #0f3460;
  --id-color: #7eb8f7;
  --tag-bg: #0f3460;
  --tag-border: #1a4a7a;
  --tag-color: #7eb8f7;
  --tag-hover: #1a4a7a;
  --copy-bg: #2a2a4a;
  --copy-hover: #3a3a5a;
  --select-border: #444466;
  --footer-bg: #0d0d1a;
  --footer-text: #666688;
  --shadow: rgba(0, 0, 0, 0.4);
}

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background-color 0.3s, color 0.3s;
}

header {
  background: linear-gradient(135deg, #4a90e2, #7b5ea7);
  color: white;
  padding: 2.5rem;
}

.header-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 600px;
  margin: 0 auto;
}

header h1 {
  font-size: 2.2rem;
  margin-bottom: 0.5rem;
}

header p {
  font-size: 1rem;
  opacity: 0.9;
}

#themeToggle {
  background: rgba(255, 255, 255, 0.2);
  border: 2px solid rgba(255, 255, 255, 0.5);
  border-radius: 50%;
  width: 2.8rem;
  height: 2.8rem;
  font-size: 1.3rem;
  cursor: pointer;
  flex-shrink: 0;
  transition: background 0.2s, transform 0.2s;
}

#themeToggle:hover {
  background: rgba(255, 255, 255, 0.35);
  transform: scale(1.1);
}

main {
  max-width: 600px;
  margin: 2rem auto;
  padding: 0 1rem;
}

section {
  background: var(--surface);
  border-radius: 12px;
  padding: 2rem;
  box-shadow: 0 4px 16px var(--shadow);
  transition: background 0.3s, box-shadow 0.3s;
}

.options {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  margin-bottom: 1.5rem;
  align-items: center;
}

.options label {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.95rem;
  cursor: pointer;
}

.options select {
  padding: 0.2rem 0.5rem;
  border: 1px solid var(--select-border);
  border-radius: 6px;
  font-size: 0.9rem;
  background: var(--surface);
  color: var(--text);
  transition: background 0.3s, color 0.3s, border-color 0.3s;
}

#generateBtn {
  width: 100%;
  padding: 0.9rem;
  background: linear-gradient(135deg, #4a90e2, #7b5ea7);
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 1.1rem;
  cursor: pointer;
  transition: opacity 0.2s;
}

#generateBtn:hover {
  opacity: 0.88;
}

#result {
  margin-top: 1.5rem;
  text-align: center;
}

#result.hidden {
  display: none;
}

.id-display {
  font-size: 2rem;
  font-weight: bold;
  color: var(--id-color);
  background: var(--id-bg);
  border-radius: 8px;
  padding: 1rem;
  margin-bottom: 0.8rem;
  letter-spacing: 1px;
  transition: background 0.3s, color 0.3s;
}

#copyBtn {
  padding: 0.5rem 1.5rem;
  background: var(--copy-bg);
  color: var(--text);
  border: none;
  border-radius: 6px;
  font-size: 0.95rem;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

#copyBtn:hover {
  background: var(--copy-hover);
}

#copyBtn.copied {
  background: #4caf50;
  color: white;
}

#history {
  margin-top: 2rem;
}

#history h3 {
  font-size: 1rem;
  color: var(--text-muted);
  margin-bottom: 0.8rem;
}

#historyList {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

#historyList li {
  background: var(--tag-bg);
  border: 1px solid var(--tag-border);
  border-radius: 20px;
  padding: 0.3rem 0.9rem;
  font-size: 0.9rem;
  color: var(--tag-color);
  cursor: pointer;
  transition: background 0.15s;
}

#historyList li:hover {
  background: var(--tag-hover);
}

footer {
  text-align: center;
  padding: 1.5rem;
  background-color: var(--footer-bg);
  color: var(--footer-text);
  font-size: 0.9rem;
  margin-top: 3rem;
  transition: background 0.3s, color 0.3s;
}