Index: src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css
===================================================================
--- src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css	(revision 58095)
+++ src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css	(working copy)
@@ -5,6 +5,7 @@
 
 .editor-styles-wrapper {
 	background: #f5efe0;
+	box-sizing: border-box;
 	color: #000;
 	letter-spacing: -0.015em;
 	-moz-font-smoothing: antialiased;
@@ -11,6 +12,10 @@
 	-webkit-font-smoothing: antialiased;
 }
 
+:where(.editor-styles-wrapper) * {
+	box-sizing: inherit;
+}
+
 .editor-styles-wrapper > * {
 	font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue", Helvetica, sans-serif;
 	font-size: 18px;
Index: src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css
===================================================================
--- src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css	(revision 58095)
+++ src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css	(working copy)
@@ -5,6 +5,7 @@
 
 .editor-styles-wrapper {
 	background: #f5efe0;
+	box-sizing: border-box;
 	color: #000;
 	letter-spacing: -0.015em;
 	-moz-font-smoothing: antialiased;
@@ -11,6 +12,10 @@
 	-webkit-font-smoothing: antialiased;
 }
 
+:where(.editor-styles-wrapper) * {
+	box-sizing: inherit;
+}
+
 .editor-styles-wrapper > * {
 	font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue", Helvetica, sans-serif;
 	font-size: 18px;