:root {
  --bg-color: #f0f0f0;
  --container-bg: #ffffff;
  --text-color: #333333;
  --shadow: 0 0 10px rgba(0, 0, 0, 0.1);
  --btn-bg: #4CAF50;
  --btn-hover: #45a049;
  --number-bg: #eee;
}

body.dark-mode {
  --bg-color: #121212;
  --container-bg: #1e1e1e;
  --text-color: #e0e0e0;
  --shadow: 0 0 15px rgba(0, 0, 0, 0.5);
  --btn-bg: #388e3c;
  --btn-hover: #2e7d32;
  --number-bg: #333;
}

body {
  font-family: sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: background-color 0.3s, color 0.3s;
  margin: 0;
}

.container {
  text-align: center;
  background-color: var(--container-bg);
  padding: 2rem;
  border-radius: 10px;
  box-shadow: var(--shadow);
  transition: background-color 0.3s, box-shadow 0.3s;
}

header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

h1 {
  margin: 0;
  font-size: 1.5rem;
}

#theme-toggle {
  background: none;
  border: 1px solid var(--text-color);
  color: var(--text-color);
  padding: 0.4rem 0.8rem;
  border-radius: 5px;
  cursor: pointer;
  font-size: 0.8rem;
  transition: all 0.3s;
}

#theme-toggle:hover {
  background-color: var(--text-color);
  color: var(--container-bg);
}

.number-display {
  display: flex;
  justify-content: center;
  margin: 1.5rem 0;
}

.number {
  display: inline-block;
  width: 40px;
  height: 40px;
  line-height: 40px;
  border-radius: 50%;
  background-color: var(--number-bg);
  margin: 0 0.5rem;
  font-size: 1.2rem;
  font-weight: bold;
  color: #fff; /* 번호 숫자는 항상 흰색 유지 (배경색 대비) */
  text-shadow: 1px 1px 2px rgba(0,0,0,0.5);
}

#generate-btn {
  padding: 0.8rem 1.5rem;
  font-size: 1rem;
  cursor: pointer;
  border: none;
  border-radius: 5px;
  background-color: var(--btn-bg);
  color: white;
  transition: background-color 0.3s;
}

#generate-btn:hover {
  background-color: var(--btn-hover);
}

footer {
  margin-top: 1.5rem;
}

footer p {
  font-size: 0.9rem;
  opacity: 0.8;
}