qr-code-component-main

I recommend that you use the flexbox properties. Your container can look like this:

.container{
    display: flex;
    flex-direction: column; /*necessary so that all your elements are in one column*/
    justify-content: center;
    align-items: center;
    margin: 0 auto;
    width: 500px;
    background-color: white;
    border-radius: 2rem;
    padding: 2rem;
    text-align: center;
    box-shadow: 0 5px 10px gray;    

}

For mobile screens I recommend changing the pixel width values ​​to percentages, so the div will adapt to any device.

@media only screen and (max-width: 500px){
    .container{
        width: 90%;
    }   
}