fix: fixed arnog#2290. isolation is required for prompts to render co…

…rrectly, but it can be on the content only

css/mathfield.less

@@ -112,6 +112,11 @@
   overflow: hidden;
   padding: 2px 3px 2px 1px;
   width: 100%;
+
+  /* Encourage the browser to use the GPU to render the field.
+     Weirdly, this is required for prompts to be rendered correctly. 
+   */
+  isolation: isolate;
 }
 
 .ML__virtual-keyboard-toggle,