style.css

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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: #daf0ff;
    font-family: 'Poppins', sans-serif;
}

#calculator {
    height: 712px;
    width: 375px;
    padding: 34px;
    background: #f7f8fb;
    border-radius: 39px;
    box-shadow: 30px 30px 30px rgba(96, 190, 255, 0.55);
}

#display {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    justify-content: center;
    height: 250px;
}

#history {
    font-size: 24px;
    line-height: 36px;
    color: #818181;
    background-color: inherit;
    border: none;
    text-align: right;
}

#result {
    font-weight: 500;
    font-size: 48px;
    line-height: 72px;
    color: #424242;
}

#keypad {
    display: grid;
    grid-template-rows: repeat(5, 62px);
    grid-template-columns: repeat(4, 62px);
    grid-gap: 20px;
}

button {
    font-size: 25px;
    font-weight: 500;
    color: #38b9ff;
    border-radius: 16px;
    background: #fff;
    border: none;
    border-radius: 1px solid #fff;
    background: linear-gradient(
        129.7deg,
        rgba(255, 255, 255, 0.6) -9.69%,
        rgba(255, 255, 255, 0.4) 114.23%
    );
}

button:hover {
    background: #eee;
}

button:active {
    background: #e2e2e2;
}