Remove dash('--') and set width of drop down menus

Is there any way to remove the dash ('--') from the drop-down menus created from using the enum property ? Is this the intended behaviour? I want to remove them from every drop down menus in json editor.

Also, how do I set the width of those drop-down menus? Well, I can remove the dash and set width by modifying the element with JavaScript but the element is not accessible if the object is in collapsed state. I'm using the json editor in 'form' mode