body {
  font-family: Arial, sans-serif;
  max-width: 400px;
  margin: 2rem auto;
  padding: 1rem;
  background: #f9f9f9;
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

h1 {
  text-align: center;
  margin-bottom: 1rem;
}

label {
  display: block;
  margin-bottom: 0.5rem;
}

#bill {
  width: 100%;
  padding: 0.5rem;
  margin-bottom: 1rem;
  font-size: 1rem;
}

.buttons {
  display: flex;
  justify-content: space-between;
  margin-bottom: 1rem;
}

.tip-btn {
  flex: 1;
  margin: 0 0.2rem;
  padding: 0.5rem;
  background: #0070f3;
  color: white;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.9rem;
}

.tip-btn:hover {
  background: #005bb5;
}

.result p {
  margin: 0.5rem 0;
  font-weight: bold;
  text-align: center;
}