*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
}

.calculator {
    display: grid;
    grid-template-columns: repeat(4, 80px);
    grid-template-rows: minmax(100px, auto) repeat(5, 80px);
    gap: 10px;
    padding: 20px;
    background-color: #333;
    border-radius: 20px;
    box-shadow: 0 10px 20px rgba(0,0,0,0.3);
}

.display {
    grid-column: 1 / -1;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    justify-content: space-around;
    padding: 10px;
    word-wrap: break-word;
    word-break: break-all;
    border-radius: 10px;
    margin-bottom: 10px;
}

.display #previous-operand {
    color: rgba(255, 255, 255, 0.7);
    font-size: 1rem;
}

.display #current-operand {
    color: white;
    font-size: 2.5rem;
}

button {
    cursor: pointer;
    font-size: 1.5rem;
    border: none;
    border-radius: 10px;
    background-color: rgba(255, 255, 255, 0.1);
    color: white;
    transition: background-color 0.2s, transform 0.1s;
}

button:hover {
    background-color: rgba(255, 255, 255, 0.2);
}

button:active {
    transform: scale(0.95);
}

.span-two {
    grid-column: span 2;
}

button[data-operation], #equals {
    background-color: #ff9f43;
}

button[data-operation]:hover, #equals:hover {
    background-color: #ff8c00;
}

#clear, #delete {
    background-color: #ff6b6b;
}

#clear:hover, #delete:hover {
    background-color: #ee5253;
}