Update subgrid to CSS 4

Author: brechtDR

list-of-css-features.md

@@ -162,6 +162,7 @@ that were discussed
 | [grid-template-areas](https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-areas) | |
 | [grid-template-columns](https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-columns) | |
 | [grid-template-rows](https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-rows) | |
+| [Subgrid](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_grid_layout/Subgrid) | |
 
 </details>
 
@@ -491,14 +492,6 @@ that were discussed
 
 </details>
 
-<details>
- <summary>Grid</summary>
-
-| Feature | Notes |
-|-------------------------------------------------------------------------------------|-------|
-| [Subgrid](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_grid_layout/Subgrid) | |
-
-</details>
 
 <details>
  <summary>Logical Properites</summary>