* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f0f0f0;
}

.calculator {
    background-color: white;
    border-radius: 10px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
    padding: 20px;
    width: 300px;
}

#display {
    width: 100%;
    height: 50px;
    font-size: 24px;
    text-align: right;
    margin-bottom: 20px;
    border: 1px solid #ccc;
    border-radius: 5px;
    padding-right: 10px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    background-color: #4CAF50;
    color: white;
    border: none;
    border-radius: 5px;
    padding: 15px;
    font-size: 18px;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.1s;
}

.btn:hover {
    background-color: #45a049;
}

.btn:active {
    transform: scale(0.95);
}

.equals {
    background-color: #2196F3;
}

.equals:hover {
    background-color: #1e88e5;
}