feat: redesign toolbar & tweaks (#4387)

src/packages/excalidraw/CHANGELOG.md

@@ -19,6 +19,8 @@ Please add the latest change on the top under the correct section.
 
 ### Features
 
+- Introduced primary colors to the app. The colors can be overriden. Check [readme](https://github.com/excalidraw/excalidraw/blob/master/src/packages/excalidraw/README.md#customizing-styles) on how to do so.
+
 - #### BREAKING CHANGE
 
   Removed `getElementMap` util method.

src/packages/excalidraw/README_NEXT.md

@@ -353,6 +353,31 @@ To view the full example visit :point_down:
 
 </details>
 
+### Customizing styles
+
+Excalidraw is using CSS variables to style certain components. To override them, you should set your own on the `.excalidraw` and `.excalidraw.theme--dark` (for dark mode variables) selectors.
+
+Make sure the selector has higher specificity, e.g. by prefixing it with your app's selector:
+
+```css
+.your-app .excalidraw {
+  --color-primary: red;
+}
+.your-app .excalidraw.theme--dark {
+  --color-primary: pink;
+}
+```
+
+Most notably, you can customize the primary colors, by overriding these variables:
+
+- `--color-primary`
+- `--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).
+
+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.
+
 ### Props
 
 | Name | Type | Default | Description |