diff --git a/core/modules/system/css/components/form.theme.css b/core/modules/system/css/components/form.theme.css
index 7ec4566..9ad86e4 100644
--- a/core/modules/system/css/components/form.theme.css
+++ b/core/modules/system/css/components/form.theme.css
@@ -96,3 +96,14 @@ abbr.ajax-changed {
   background: url(../../../../misc/icons/e32700/error.svg) no-repeat;
   background-size: contain;
 }
+
+/* Style for image dialog form. */
+.editor-image-dialog .form-composite > legend {
+  float: left;
+  margin-right: 1em;
+}
+
+[dir="rtl"] .editor-image-dialog .form-composite > legend {
+  float: right;
+  margin-left: 1em;
+}