style.css

@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@500&display=swap');

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: "Poppins", sans-serif;
}

body {
    width: 100%;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background-repeat: no-repeat;
    background: linear-gradient(45deg, #81e481, #fc9fe5);
}

.calculator {
    border: 1px solid #717377;
    padding: 20px;
    border-radius: 16px;
    background: #fff;
    border: 1px solid #64a0d4;
    box-shadow: 10px 10px 10px rgba(89, 157, 240, 0.927);
}

input {
    width: 320px;
    border: none;
    padding: 24px;
    margin: 10px;
    background: #d8eafa;
    text-align: right;
    font-size: 40px;
    cursor: pointer;
    color: #000000;
    border-radius: 5px;
    box-shadow: 5px 5px 8px rgba(134, 181, 238, 0.927);
}

input::placeholder {
    color: #000000;
}

button {
    width: 60px;
    height: 60px;
    margin: 10px;
    border-radius: 50%;
    background: #d8eafa;
    color: #74757d;
    font-size: 20px;
    border: none;
    font-weight: 500;
    cursor: pointer;
    box-shadow: 5px 5px 8px rgba(134, 181, 238, 0.927);
}

button:hover {
    color: #ffffff;
    background: #469ce8;
}

.equalbtn {
    background: #84c9f0;
}

.operator {
    color: #0869d8;
}

.operator:hover {
    color: #ffffff;
    background: #0c6abd;
}

@media (max-width:768px) {
    .calculator {
        padding: 10px;
    }
}