fix: rename --color-primary-chubb to --color-primary-contrast-offset and fallback to primary color if not present (#4803)

* fix: fallback to primary color if --color-primary-chubb not present

* rename to --color-primary-contrast-offset

* use contarst-offset

Co-authored-by: David Luzar <luzar.david@gmail.com>

* Update src/packages/excalidraw/README_NEXT.md

* remove

* Update src/packages/excalidraw/README_NEXT.md

Co-authored-by: David Luzar <luzar.david@gmail.com>

Co-authored-by: David Luzar <luzar.david@gmail.com>

src/packages/excalidraw/README_NEXT.md

@@ -374,7 +374,7 @@ Most notably, you can customize the primary colors, by overriding these variable
 - `--color-primary-darker`
 - `--color-primary-darkest`
 - `--color-primary-light`
-- `--color-primary-chubb` — a slightly darker (in light mode), or lighter (in dark mode) `--color-primary` color to account for [Chubb illusion](https://en.wikipedia.org/wiki/Chubb_illusion).
+- `--color-primary-contrast-offset` — a slightly darker (in light mode), or lighter (in dark mode) `--color-primary` color to fix contrast issues (see [Chubb illusion](https://en.wikipedia.org/wiki/Chubb_illusion)). It will fall back to `--color-primary` if not present.
 
 For a complete list of variables, check [theme.scss](https://github.com/excalidraw/excalidraw/blob/master/src/css/theme.scss), though most of them will not make sense to override.
 

src/packages/excalidraw/example/App.scss

@@ -40,3 +40,10 @@
     display: flex;
   }
 }
+
+.excalidraw {
+  --color-primary: #faa2c1;
+  --color-primary-darker: #f783ac;
+  --color-primary-darkest: #e64980;
+  --color-primary-light: #fcc2d7;
+}