(core) Improve dark mode

Summary:
Enhances dark mode support for the formula editor, and adds support to
the color select popup. Also fixes some bugs with dark mode.

Test Plan: Tested manually.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3847

app/client/widgets/ConditionalStyle.ts

@@ -186,7 +186,7 @@ export class ConditionalStyle extends Disposable {
   ) {
     return cssFieldFormula(
       formula,
-      { maxLines: 1 },
+      { gristTheme: this._gristDoc.currentTheme, maxLines: 1 },
       dom.cls('formula_field_sidepane'),
       dom.cls(cssErrorBorder.className, hasError),
       { tabIndex: '-1' },