I have a SharePoint site and list with a nintex form. I add a panel, give it styles like borders and background color, however the border never shows up. I have it at 4px thickness, colors that should show up, and have gotten rid of any custom css on the form.why wouldn't it show up?
Borders missing from controls
+17@momitaskhan can you share a screenshot of your form and the configuration for the panel? I was able to test this on a form and everything worked fine. 
Are you using the out of the box border styling control or are you doing that with CSS in the form settings?
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