Please look at this example https://www.jeasyui.com/demo/main/index.php?plugin=Tabs&theme=material-teal&dir=ltr&pitem=Tab%20Position&sort=asc

I had looked this,the same bug.
You try to change the Position between "top" and "left".

Tabs's bug:
when Tabs's Position is set to "left" or "right" that the first tab will not show full
I don't know if my description is enough.
Maybe my code's problem...