Responsive CSS and HTML

@Wandesanguine Your solution is perfect (for mobile view) you could use display: flex & media querie to make .containner responsive :

@media (min-width:400px){
     .containner{
       display:flex;  
       justify-content: center; 
         =>to stack the .group1, .group2 and .group3 horizontally
                                    }
   .body{  
   height:100vh; =>  set the body height to the screen height
   display:flex;
   flex-direction:columns ; =>  to stack the  body  on top of the  footer
    align-items: center;  =>  to center the  body  vertically
    justify-content: center;  => to center   body  horizontally
                           }
               }```
              
After this you can adjust the borders, background etc 
happy coding