Incorporate rulers into the sketch preview pane

[iamjessklein]

As per the issue that I started over in the p5.js website repo, it would be great to add rulers to the sketch preview pane to help learners orient themselves within the sketch. I'm wondering if the widget would be an appropriate place to experiment with this interaction.

[iamjessklein]

Building off of the widget that's currently implemented, I did a few iterations on the style.

Here's the current implementation:

Here are my first iterations:

Option A:

Option B:

Option C:

Please provide feedback on this invision mockup.