OK, so it’s literally just for decoration?
Best case scenario would be to set up an SVG to sit there for you. You could use any number of graphical editors, and then just put the image into a container that is 50% the width of the parent and voilà.
Technically, you could do it with HTML/CSS… but you certainly wouldn’t want to do it with your original idea. You’re mixing presentation and design which is a big no-no.
Here’s an ugly way of doing it (you’d just need to change colors, I also didn’t do much for responsive testing of edge cases):