diff --git a/client/post-editor/editor-html-toolbar/style.scss b/client/post-editor/editor-html-toolbar/style.scss
index a248256191b4d..75b42d30df2b5 100644
--- a/client/post-editor/editor-html-toolbar/style.scss
+++ b/client/post-editor/editor-html-toolbar/style.scss
@@ -48,6 +48,17 @@
 			width: calc( 100% - ( #{ ( $sidebar-width-max * 2 ) + 1 } ) );
 			left: 0;
 		}
+
+		@include breakpoint( "660px-960px" ) {
+			.focus-sidebar &,
+			.has-chat & {
+				width: calc( 100% - ( #{ $sidebar-width-min + 1 } ) );
+			}
+
+			.focus-sidebar.has-chat & {
+				width: calc( 100% - ( #{ ( $sidebar-width-min * 2 ) + 1 } ) );
+			}
+		}
 	}
 
 	.editor-html-toolbar__wrapper-buttons {