Formatting profile page, CSS, HTML etc

We're struggling to format our profile page so that embedded images work nicely on both desktop and mobile. 

Any CSS we add with the editing tool is stripped out, allowing only HTML properties on the images - which don't allow settings for both width and max width.

We've just uploaded a couple new images of the studio, and we'd like to have these displayed at the full container width within the profile page. If we set width="100%" on desktop, this pushes the images down past any of the floating elements on the right, but looks perfect on mobile. If we take away that HTML property, it displays perfectly on the site at the original size, but then it's huge on mobile - and I assume that the container is set to overflow: hidden or similar as there's no way to horizontal scroll to see the full image.

An easy fix for this which would be site-wide would be to add the CSS to any images in the page content to be max-width:100%

This is how it displays on mobile with and without width set to 100%: