Add comment to explain front-end-only selector.

packages/block-editor/src/components/global-styles/use-global-styles-output.js

@@ -664,6 +664,10 @@ export const toStyles = (
 	}
 
 	if ( useRootPaddingAlign ) {
+		/*
+		 * These rules reproduce the ones from https://github.com/WordPress/gutenberg/blob/79103f124925d1f457f627e154f52a56228ed5ad/lib/class-wp-theme-json-gutenberg.php#L2508
+		 * almost exactly, but for the selectors that target block wrappers in the front end. This code only runs in the editor, so it doesn't need those selectors.
+		 */
 		ruleset += `padding-right: 0; padding-left: 0; padding-top: var(--wp--style--root--padding-top); padding-bottom: var(--wp--style--root--padding-bottom) }
 			.has-global-padding { padding-right: var(--wp--style--root--padding-right); padding-left: var(--wp--style--root--padding-left); }
 			.has-global-padding :where(.has-global-padding) { padding-right: 0; padding-left: 0; }