body {
  margin: 0;
  font-family: 'Segoe UI', sans-serif;
  background: #f9f9f9;
  color: #333;
  transition: background 0.5s, color 0.5s;
}

body.dark {
  background: #121212;
  color: #f0f0f0;
}

.container {
  max-width: 600px;
  margin: 3rem auto;
  padding: 2rem;
  background: rgba(255,255,255,0.9);
  border-radius: 12px;
  box-shadow: 0 0 16px rgba(0,0,0,0.1);
}

body.dark .container {
  background: rgba(18, 18, 18, 0.95);
}

h1 {
  text-align: center;
  margin-bottom: 1.5rem;
}

form label {
  display: block;
  margin: 1rem 0 0.3rem;
}

input[type="text"],
input[type="number"],
textarea {
  width: 100%;
  padding: 0.6rem;
  border: 1px solid #ccc;
  border-radius: 6px;
  font-size: 1rem;
  box-sizing: border-box;
}

button {
  margin-top: 1rem;
  padding: 0.7rem 1.2rem;
  font-size: 1rem;
  background: #007bff;
  color: white;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: background 0.3s;
}

button:hover {
  background: #0056b3;
}

.actions {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 1rem;
}

textarea {
  margin-top: 1rem;
  height: 200px;
  resize: vertical;
  font-family: monospace;
}

footer {
  text-align: center;
  margin-top: 2rem;
  font-size: 0.9rem;
  opacity: 0.7;
}

.options label {
  display: inline-block;
  margin-right: 1rem;
  font-weight: normal;
}

/* Toggle Dark Mode */
.toggle-dark {
  position: fixed;
  top: 1rem;
  right: 1rem;
  cursor: pointer;
}

/* Mưa rơi */
.raindrop {
  position: fixed;
  width: 2px;
  height: 15px;
  background: #00f3ff;
  top: -20px;
  animation: fall 1s linear infinite;
  opacity: 0.4;
}

@keyframes fall {
  to {
    transform: translateY(120vh);
    opacity: 0;
  }
}