Help reversing html code I entered

Hello,

I thought I wanted every link to open in a new window, but after trying it, I'm wrong. Everything I click on opens a new window including every page and category.

I entered <base target="main"> in the header section using the HTML/CSS Insert feature. I would like to take it out, but how? Or do I enter a new line of html that cancels it out?

I'm a beginner (clearly) so my skills are very limited. I don't want to break anything...

Thank you in advance.