small screens, fixed toolbar and media queries

I had a problem with the toolbar menu making my site body smaller at smaller screen sizes. So if I've made my responsive theme according to screen size then after logging in and at certain screen sizes the layout would be too narrow and I would have to add more complexity to my css. Trying to find the easy way (do the responsive css once) I wanted to just force the theme to mobile if that vertical menu is active. I've done this by adding a class - toolbar-vertical-not-forced-fixed - to body (both js and html.html.twig) that is only active if the screen is not at the problematic size. My css looks like this

// Mobile first.
body {
  background: red;
}

.toolbar-vertical-not-forced-fixed {
  // Tablet
  @media ...

  // Desktop
  @media ...
}

So if the vertical menu is active then the site is always in mobile state.