Index: wp-content/themes/twentynineteen/style-editor.scss
===================================================================
--- wp-content/themes/twentynineteen/style-editor.scss	(revision 55900)
+++ wp-content/themes/twentynineteen/style-editor.scss	(working copy)
@@ -1020,3 +1020,9 @@
 		width: 100%;
 	}
 }
+
+.wp-block-read-more {
+	display:block;
+	width:-moz-fit-content !important;
+	width:fit-content !important;
+}
\ No newline at end of file