[css-forms-1] Use visibility for checkmark (#13555)

Author: lukewarlow

css-forms-1/Overview.bs

@@ -886,16 +886,21 @@ input[type=radio] {
     justify-content: center;
 }
 
-input[type=radio] {
-    border-radius: 50%;
+input[type=checkbox]:not([switch])::checkmark,
+input[type=radio]::checkmark {
+    content: '\2713' / '';
 }
 
-input[type=checkbox]:not([switch]):checked::checkmark {
-    content: '\2713' / '';
+input[type=checkbox]:not([switch], :checked)::checkmark {
+input[type=radio]:not(:checked)::checkmark {
+    visibility: hidden;
+}
+
+input[type=radio] {
+    border-radius: 50%;
 }
 
 input[type=radio]:checked::checkmark {
-    content: '';
     background-color: currentColor;
     display: inline-block;
     border-radius: inherit;