[ci skip] Update supported units described in theme CSS docs: Order u…

…nits by alphabetical

docs/theme-css.md

@@ -93,7 +93,7 @@ section {
 }
 ```
 
-!> Please notice _it must define **the static length in an absolute unit.**_ We support `cm`, `in`, `mm`, `pc`, `pt`, `Q`, and `px`.
+!> Please notice _it must define **the static length in an absolute unit.**_ We support `cm`, `in`, `mm`, `pc`, `pt`, `px`, and `Q`.
 
 ?> It is determined **one size per theme** in Marpit. The slide size cannot change through using [inline style](#tweak-style-through-markdown), [custom class](/directives#class), and [CSS custom property](https://developer.mozilla.org/en-US/docs/Web/CSS/--*). But the width of contents may shrink if user was using [split backgrounds](/image-syntax#split-backgrounds).