[TASK]: clean up the --gap variables

[YohannParis]

Describe the task
We have an incomplete list of gap, margin, and padding variables and not all applied.
Their is a lack of consistency in the CSS and it's a mess.

Task Items

• Find all the potential values used in the application .25rem, .5rem, .75rem, etc
• Check if Tailwind already offers those values
• Update the CSS variables to a up to date list of gaps, from XXS to XXL maybe

Goal
This needs to be done in a one swoop and the merge commit id should be added to the ignore list.
https://github.com/DARPA-ASKEM/terarium/blob/main/.github/CONTRIBUTING.md#ignore-commits-in-the-blame-view