The implementation and CSS classes for custom modal formats differs, depending upon whether your application is rendered in HTML5 document type - standards mode or in quirks mode. For example, in HTML5 document type – standards mode, modal dialogs honor the design time width of the layout, while, in quirks mode, modal dialogs shrink to the minimum width and height possible. Drag and drop is not supported in modal dialogs rendered in standards mode. If your application contains modal dialogs and is rendered in both standards and quirks modes, generate test cases for each. See Displaying a modal dialog in a custom format created in the skin on the Pega Community.