:root {
  --bg-color: #f0f0f2;
  --container-bg: #ffffff;
  --text-color: #333333;
  --btn-bg: #4a90e2;
  --btn-text: #ffffff;
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
}

body.dark {
  --bg-color: #1a1a1a;
  --container-bg: #2d2d2d;
  --text-color: #f0f0f0;
  --btn-bg: #357abd;
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

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

.container {
  text-align: center;
  background-color: var(--container-bg);
  padding: 3rem 2rem;
  border-radius: 20px;
  box-shadow: var(--shadow);
  width: 90%;
  max-width: 400px;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

h1 {
  margin-bottom: 2rem;
  font-weight: 700;
}

#generate-btn {
  padding: 0.8rem 2rem;
  font-size: 1.1rem;
  font-weight: 600;
  cursor: pointer;
  background-color: var(--btn-bg);
  color: var(--btn-text);
  border: none;
  border-radius: 12px;
  transition: transform 0.2s ease, background-color 0.2s ease;
}

#generate-btn:active {
  transform: scale(0.95);
}

#numbers-container {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 2rem;
  min-height: 50px;
}

.number {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 45px;
  height: 45px;
  border-radius: 50%;
  font-size: 1.1rem;
  font-weight: 700;
  color: #fff;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  animation: pop 0.3s ease-out forwards;
}

@keyframes pop {
  0% { transform: scale(0.5); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}

.theme-toggle {
  position: fixed;
  top: 20px;
  right: 20px;
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  color: var(--text-color);
  padding: 10px;
  border-radius: 50%;
  background-color: var(--container-bg);
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background-color 0.3s ease;
}