What is this line?

[Pepe]

Hi, I am new to making themes here - what is this line beside subject and poll icon and how do i get rid of it please and thankyou.

[Kami]

That is the container for the checkbox. If you hover over it, it should appear. This checkbox is a necessary function to select threads for moderation purposes (locking, deleting, etc). I don't advise getting rid of it unless you're OK with being unable to moderate threads on the thread list and the accompanying requirement to edit individual threads by editing the opening post of each thread one at a time (though note you cannot delete entire threads via editing the opening post).

[Pepe]

ok thank you.

edit to add it was my error - i had borders where i shouldn't have.

[Kami]

You're welcome! (: