Add html to reset styles on the editor-styles-wrapper container

Also removes comment about not needing it within an iframe.

packages/block-library/src/reset.scss

@@ -8,19 +8,18 @@
 // We use :where to keep specificity minimal.
 // https://css-tricks.com/almanac/selectors/w/where/
 :where(.editor-styles-wrapper) {
-	/**
-	* The following styles revert to the browser defaults overriding the WPAdmin styles.
-	* This is only needed while the block editor is not being loaded in an iframe.
-	*/
-	font-family: serif; // unfortunately initial doesn't work for font-family.
-	font-size: initial;
-	line-height: initial;
-	color: initial;
+	// The following styles revert to the browser defaults overriding the WPAdmin styles.
+	html & {
+		font-family: serif; // unfortunately initial doesn't work for font-family.
+		font-size: initial;
+		line-height: initial;
+		color: initial;
 
-	// Many themes with white backgrounds load editor styles but fail to also provide
-	// an explicit white background color, assuming a white editing canvas.
-	// So to match browser defaults, we provide a white default here as well.
-	background: #fff;
+		// Many themes with white backgrounds load editor styles but fail to also provide
+		// an explicit white background color, assuming a white editing canvas.
+		// So to match browser defaults, we provide a white default here as well.
+		background: #fff;
+	}
 
 	.wp-align-wrapper {
 		max-width: $content-width;