body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #667eea, #764ba2);
  color: #fff;
  text-align: center;
  padding: 50px;
  transition: all 0.3s ease-in-out;
  min-height: 100vh;
}
.container {
  background-color: rgba(0,0,0,0.2);
  padding: 30px;
  border-radius: 15px;
  width: 90%;
  max-width: 350px;
  margin: auto;
  box-shadow: 0 4px 15px rgba(0,0,0,0.3);
  animation: fadeIn 1s ease-in-out;
}
input[type="date"] {
  padding: 10px;
  margin: 15px 0;
  border: none;
  border-radius: 5px;
  width: 100%;
}
button {
  padding: 10px 20px;
  background-color: #ff6a00;
  color: #fff;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}
button:hover {
  background-color: #e65c00;
}
#result {
  margin-top: 20px;
  font-size: 1.2em;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}
#theme-toggle {
  position: absolute;
  top: 20px;
  right: 20px;
  padding: 8px 12px;
  border: none;
  background-color: #fff;
  color: #000;
  border-radius: 5px;
  cursor: pointer;
  transition: background 0.3s ease;
}
body.light {
  background: linear-gradient(135deg, #f5f7fa, #c3cfe2);
  color: #333;
}
body.light .container {
  background-color: rgba(255, 255, 255, 0.8);
  color: #000;
}
body.light button {
  background-color: #333;
  color: #fff;
}
body.light button:hover {
  background-color: #555;
}
body.light #theme-toggle {
  background-color: #000;
  color: #fff;
}