style.css

body {
    background-image: url("https://st.depositphotos.com/1278966/1959/i/950/depositphotos_19597183-stock-photo-school-math-drawing-tools-background.jpg");
    background-size: 1500px 800px;
    background-repeat: no-repeat;
}

.container {
    text-align: center;
    margin-top: 23px
}

table {
    margin: auto;
}

input {
    border-radius: 21px;
    border: 5px solid black;
    font-size: 34px;
    height: 65px;
    width: 456px;
}

button {
    border-radius: 20px;
    font-size: 40px;
    background: black;
    color: white;
    width: 90px;
    height: 60px;
    margin: 6px;
}

.calculator {
    border: 4px solid black;
    background-color: rgb(106, 165, 233);
    padding: 23px;
    border-radius: 90px;
    display: inline-block;

}

h1 {
    font-size: 60px;
    font-family: 'Courier New', Courier, monospace;
}