[Izkata]

You'd do it with media queries and make different grids for different screen sizes. If anything it's more flexible than bootstrap because you can change element order as well.

[lagt_t]

https://getbootstrap.com/docs/5.3/layout/columns/#reordering

Bootstrap grid system is super complete, and probably better coded that anything I can make. Its also available as a standalone module, so the size is pretty small. I just wanted it integrated to PicoCSS because I'm lazy.

[Izkata]

A really quick example of switching between desktop and mobile page layouts at 800px:

  @media (min-width: 800px) {
     #page {
        grid-template-areas:
           "header header"
           "menu   content"
           "footer footer";
     }
  }
  @media (max-width: 800px) {
     #page {
        grid-template-areas:
           "header  menu"
           "content content"
           "footer  footer";
     }
  }