Here's my demo page:
About the HTML:
Again, I mostly used standard building blocks for this.
Currently, I use a new colscheme-2-2nd-narrow with a 2/3 : 1/3 proportion for the column widths. I have to see how this works out once the special viewer are put in. I might still define an overflow-x: hidden for the .view-columns to make the layout work for smaller viewports. Another option is a fixed-fluid-width setup but that's tricky.
I would definitely make the Stimulus diagrams less wide as I figure the shape of the curve carries the most important information anyway. Currently, they're 600px wide. I would cut back to 400px.
The only special element is an ul.focal-points: Here, the vertex management takes place. As we're dealing w/ up to 20 vertices, I moved the whole thing above the viewer (where the user selects vertices anyway) and made it much more space-economical.
2 things I noticed:
:: There are a couple of equation fields in the SpaceTime forms, set to "readonly". The shouldn't be marked as .field-mandatory then.
:: There's another readonly field in the SurfaceStim form, listing the currently selected focal points. Isn't that superfluous as we have a focal point management anyway?