I get a solid line across the top

[DreamITSoftware]

It looks like it's trying to draw, but doesn't create the tabs.

[DreamITSoftware]

No errors in the console

[DreamITSoftware]

Cleared my cache, it's looking a bit better

[aricbost]

Try saving the page then applying the webpart and closing the modify panel. That solved it for me.