style.css

*{
    margin: 0;
    padding: 0;
}
.navbar{
    background-color: black;
    color: white;
    padding: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 30px;
}
.main{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 85vh;
    background-color: #555269;
}
.container{
    size: auto;
    background-color: white;
    border: 4px solid black;
    border-radius: 9px;
    padding: 15px 15px;
}
input{
    margin: 10px 10px;
    background-color: transparent;
    height: 50px;
    width: 97%;
    box-sizing: border-box;
    border-radius: 9px;
    font-size: 30px;
    text-align: end  ;
}
button{
    position: relative;
    box-sizing: border-box;
    width: 60px;
    height: 35px;
    font-size: 15px;
    font-weight: bold;
    text-align: center;
    border: 2px solid black;
    border-radius: 7px;
    cursor: pointer;
    margin: 2px;
}
#equals, #clear, #back{
    background-color: #181734;
    color: white;
}
#equals:active, #clear:active, #back:active{
    background-color: #555269 ;
}
button:active{
    background-color: #555269 ;
} 
.btnNum{
    font-size: 25px;
    padding-top: 2px;
    padding-bottom: 2px;
    width: 69px;
    height: 38px;
}
footer{
    color: white;
    background-color: black;
    display: flex;
    justify-content: center;
    align-items: center;
}