Issue #3270139 by jannakha, bnjmnm, smustgrave, mgifford: CKEditor admin...

Issue #3270139 by jannakha, bnjmnm, smustgrave, mgifford: CKEditor admin toolbar config buttons using ::before to add content: have invalid screen reader text

core/modules/ckeditor5/css/essentials.admin.css

 .ckeditor5-toolbar-button-divider {
   background-image: url(../icons/divider.svg);
 }
+
 .ckeditor5-toolbar-button-wrapping {
   background-image: url(../icons/separator.svg);
 }
@@ -20,15 +21,20 @@
   width: 100px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-heading::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Heading";
+  content: "Heading" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-heading::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-heading::after {
   display: inline-block;
   width: 7px;
@@ -39,6 +45,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-heading::after {
   margin-right: 0;
   margin-left: 10px;

core/modules/ckeditor5/css/language.admin.css

@@ -5,15 +5,20 @@
   width: 110px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-textPartLanguage::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Language";
+  content: "Language" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-textPartLanguage::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-textPartLanguage::after {
   display: inline-block;
   width: 7px;
@@ -24,6 +29,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-textPartLanguage::after {
   margin-right: 0;
   margin-left: 10px;

core/modules/ckeditor5/css/style.admin.css

@@ -5,15 +5,20 @@
   width: 110px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-style::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Style";
+  content: "Style" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-style::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-style::after {
   display: inline-block;
   width: 7px;
@@ -24,6 +29,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-style::after {
   margin-right: 0;
   margin-left: 10px;