remove border, use padding top/bottom

packages/block-editor/src/components/iframe/content.scss

@@ -19,9 +19,7 @@
 
 	background-color: $gray-300;
 
-	// Firefox and Safari don't render margin-bottom here and margin-bottom is needed for Chrome
-	// layout, so we use border matching the background instead of margins.
-	border: calc(#{$frame-size} / #{$scale}) solid $gray-300;
+	padding: calc(#{$frame-size} / #{$scale}) 0;
 
 	// Chrome seems to respect that transform scale shouldn't affect the layout size of the element,
 	// so we need to adjust the height of the content to match the scale by using negative margins.