style.css

* {
    box-sizing: border-box;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    
}

.calculator {
    width: 350px;
    height: 500px;
    /* border: 2px solid red; */

    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;

    background-color: black;

}

.result {
    /* border: 2px solid blue; */
    width: 300px;
    height: 150px;

    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: center;
}

.result_value {

    margin-bottom: 10px;
    text-align: right;
    font-size: 60px;
    width: 220px;
    height: 50px;

    background-color: black;
    border: 0px;

}

input::placeholder {
    color:white
}


.input {
    /* border: 2px solid blue; */
    width: 300px;
    height: 300px;    
    
    display: flex;
    flex-direction: column;
    justify-content: space-evenly;
    align-items: center;

}

.input_box {
    /* border: 2px solid green; */
    width: 250px;
    height: 50px;

    display: flex;
    justify-content: space-evenly;

}

.btn {

    width: 50px;
    height: 50px;
    border-radius: 50%;
    font-size: 25px;
    border: 0px;
}

#btn_0 {
    width: 110px;
    height: 50px;
    border-radius: 50px;
    font-size: 30px;
    text-align: left;
    border: 0px;

    padding-left: 18px;

    background-color: rgb(91, 90, 90);
    color: white;
}

#btn_white_gray {
    background-color: rgb(220, 218, 218);
}

#btn_yellow {
    background-color: rgb(245, 178, 54);
    color: white;
}

#btn_dark_gray {
    background-color: rgb(91, 90, 90);
    color: white;
}