[csswg-drafts] [css-sizing-4] Add example for how %-block-size percentages resolve for min/max size calculation. (#4639)

bfgeek has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-sizing-4] Add example for how %-block-size percentages resolve for min/max size calculation.  ==
E.g.
```html
<div id=container style="height: 100px; float: left;">
  <div style="height: 100%; aspect-ratio: 1/1;"></div>
</div>
```

The width of "container" should be 100px(?). Adding an example would be helpful.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4639 using your GitHub account