Responsive outline? - Visual composer - #may1reboot : First of all, may the first be with you!

Now for my question. As always I started too late with fixing up my work. I'm trying to create an outline like in the attached image ([![examplepage][1]][1]). So far so good, the outline works and the outline-offset too.

But: in it's current state it is not responsive in any way (because of the way I gave the CSS), my knowledge just isn't on par yet, still learning though!

Is there any way I can set the outline-offset to percentages?

Current solution:

    outline: 5px solid #ccc;
    outline-offset: -50px;


  [1]: https://i.stack.imgur.com/hQUyv.jpg