body {
  margin: 0;
  font-family: Arial;
  background: #f4f6f8;
  text-align: center;
}

#topbar {
  background: #2c3e50;
  color: white;
  padding: 10px;
  font-weight: bold;
}

#app {
  padding: 20px;
}

h1 {
  margin-top: 10px;
}

button {
  display: block;
  width: 90%;
  max-width: 320px;
  margin: 10px auto;
  padding: 14px;
  font-size: 16px;
  border: none;
  border-radius: 12px;
  background: white;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

#levelup {
  position: fixed;
  top: 40%;
  left: 50%;
  transform: translate(-50%);
  background: gold;
  padding: 20px;
  border-radius: 12px;
  display: none;
  font-weight: bold;
}