Style: Make components themeable (#5908)

## Summary

Replace color/dark-color pairs in components with design tokens to allow
for easy overriding.
<!-- Also standardizes the icon pattern to simplify the tailwind config.
-->

## Changes

- **What**: Token based colors, for now, mostly.
- **Breaking**: Got approval from Design to collapse some very similar
pairs of colors that seem to have diverged in implementations over time.
Some of the colors might be a little different, but we can tweak them
later.

## Review Focus

Still have quite a few places from which to remove `dark-theme`, but
this at least gets the theming much closer.
Need to decide if I want to keep going in here or cut this and do the
rest in a subsequent PR.

## Screenshots (if applicable)

<!-- Add screenshots or video recording to help explain your changes -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5908-WIP-Make-components-themeable-2816d73d365081ffbc05d189fe71084b)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

browser_tests/tests/vueNodes/nodeStates/collapse.spec.ts

@@ -50,17 +50,17 @@ test.describe('Vue Node Collapse', () => {
 
     // Check initial expanded state icon
     let iconClass = await vueNode.getCollapseIconClass()
-    expect(iconClass).toContain('pi-chevron-down')
+    expect(iconClass).not.toContain('-rotate-90')
 
     // Collapse and check icon
     await vueNode.toggleCollapse()
     iconClass = await vueNode.getCollapseIconClass()
-    expect(iconClass).toContain('pi-chevron-right')
+    expect(iconClass).toContain('-rotate-90')
 
     // Expand and check icon
     await vueNode.toggleCollapse()
     iconClass = await vueNode.getCollapseIconClass()
-    expect(iconClass).toContain('pi-chevron-down')
+    expect(iconClass).not.toContain('-rotate-90')
   })
 
   test('should preserve title when collapsing/expanding', async ({