Restrict width of Gallery Page Images on Supply Template

Site URL: https://constantinetohme.com/treatments

Can anyone help me I'm trying to restrict the width of 'gallery page' images on Supply template - [here] is an example of a 'gallery page' - where images are displayed vertically with text shown on the right. Does anyone know custom CSS i can use to restrict the width of those images? I just want the images to be narrower and restricted/custom width.

I've tried different css but can't seem to figure it out... what's worse is when the browser window is made full screen the image also scales up and increases the width, distorting and just taking up more of the page then I want it to.

Any CSS advice to fix that really appreciated! Thanks