Calc.css

* {
    padding: 0;
    margin: 0;
    font-family: 'poppins', sans-serif;
}

body {
    background-color: #4a8a7caf;
    display: grid;
    height: 100vh;
    place-items: center;
}

.main {
    width: 400px;
    height: 450px;
    background-color: rgba(58, 70, 46, 0.568);
    position: absolute;
    border: 5px solid rgb(0, 0, 0);
    border-radius: 6px;
}

.main input[type='text'] {
    width: 90%;
    position: relative;
    height: 50px;
    top: 10px;
    text-align: right;
    padding: 3px 6px;
    outline: none;
    font-size: 40px;
    border: 5px solid black;
    display: flex;
    margin: auto;
    border-radius: 6px;
    color: black;
}

.btn input[type='button'] {
    width: 90px;
    padding: 2px;
    margin: 7px 0px;
    position: relative;
    left: 13px;
    top: 20px;
    height: 50px;
    cursor: pointer;
    font-size: 16px;
    transition: 0.5s;
    background-color: #495250;
    border-radius: 6px;
    color: white;
}

.btn input[type='button']:hover {
    background-color: black;
    color: white;
}