Add .dark-mode-invert class to darken bright images in dark mode (#2253)

- Apply div.dark-mode-invert to image in README.md

This might not be the best way to add a dark mode class to but I
couldn't figure out how to get tailwind classes into the `.md` files.

Pretty much same thing could be achieved with `class="invert
hue-rotate-180"` if tailwind classes were recognizable in the
`.md`/`.mdx` files.

## Checklist

- [ ] I have added
[tests](https://www.cursorless.org/docs/contributing/test-case-recorder/)
- [ ] I have updated the
[docs](https://github.com/cursorless-dev/cursorless/tree/main/docs) and
[cheatsheet](https://github.com/cursorless-dev/cursorless/tree/main/cursorless-talon/src/cheatsheet)
- [ ] I have not broken the cheatsheet

<details>
<summary>Screenshot before PR</summary>
<img width="1100" alt="image"
src="https://github.com/cursorless-dev/cursorless/assets/5898009/948b64f0-4f35-40c2-83d6-99f0ee03e8e6">

</details>

<details>
<summary>Screenshot after PR</summary>
<img width="1100" alt="image"
src="https://github.com/cursorless-dev/cursorless/assets/5898009/d7fd701a-71e3-4607-8792-6922dd6d3ea7">

</details>

Author: trillium

docs/user/README.md

@@ -184,7 +184,9 @@ We support several modifiers that allow you to refer to scopes relative to the i
 
 Here is a diagram of the possible relative / ordinal modifiers using the `funk` scope as an example:
 
-![Relative ordinal diagram](images/relative_ordinal.png)
+<div class="dark-mode-invert">
+  ![Relative ordinal diagram](images/relative_ordinal.png)
+</div>
 
 ([Image source](https://github.com/cursorless-dev/cursorless/blob/main/docs/user/images/relative_ordinal.tex))
 

packages/cursorless-org-docs/src/css/custom.css

@@ -16,3 +16,7 @@
   background: url("data:image/svg+xml,%3Csvg viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath fill='white' d='M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12'/%3E%3C/svg%3E")
     no-repeat;
 }
+
+[data-theme="dark"] .dark-mode-invert {
+  filter: invert(90%) hue-rotate(180deg);
+}