* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 0;
    font-family: 'Arial', sans-serif;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}

button {
    width: 70px;
    height: 60px;
    margin: 5px;
    padding: 0;
    background-color: aliceblue;
    border: none;
    font-size: 18px;
    font-weight: bold;
    border-radius: 8px;
    cursor: pointer;
    box-shadow: 0 3px 8px rgba(0, 0, 0, 0.2);
}

#backspace {
    width: 150px;
    font-size: 14px;
}

.sign {
    background-color: #ff9500;
    color: white;
}

.sign:hover {
    background-color: #e6850e;
}

#clear, #backspace {
    background-color: #ff6b6b;
    color: white;
}

#clear:hover, #backspace:hover {
    background-color: #ff5252;
}

#showResult {
    background-color: #4ecdc4;
    color: white;
    width: 150px;
}

#showResult:hover {
    background-color: #26a69a;
}

#screen {
    font-size: 24px;
    width: 320px;
    height: 60px;
    margin: 20px auto;
    display: flex;
    justify-content: flex-end;
    align-items: center;
    background-color: #2c3e50;
    color: white;
    border-radius: 8px;
    padding: 0 15px;
    word-wrap: break-word;
    overflow: hidden;
}

.calculator {
    max-width: 400px;
    padding: 20px;
    border-radius: 15px;
    background-color: #34495e;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
}

.btn-row {
    display: flex;
    justify-content: center;
    margin: 5px 0;
}

.number {
    background-color: #ecf0f1;
    color: #2c3e50;
}

.number:hover {
    background-color: #bdc3c7;
}

.zero {
    width: 150px;
}