CSS HTML

What you did is correct. You need to add the border on the buttons when hover.

@media only screen and (max-width: 575px) {

     body{
        padding: 1rem 0;
     }

    .container{
/*         display: flex; */ /* you don't need to repeat this, you already have this above */
        flex-direction: column;
/*         align-items: center; */ /* don't need to repeat this also */
        border-radius: 0.5rem;
    }
    
}