In the header for the answers sections, there are kinks in the line:

where there are not on, say, Stack Overflow:

It is the same in both Firefox 46.0 and IE11.

Perhaps someone could tweak the CSS for electronics.stackexchange?

• Don't you have something better to do? – Olin Lathrop Apr 29 '16 at 10:46
• Here are EEs that love kinks... – PlasmaHH Apr 29 '16 at 10:48
• @OlinLathrop What could possibly be better than making this site better? /me goes back to refactoring code in a noisy office. – Andrew Morton Apr 29 '16 at 10:50
• Well, this certainly isn't the post I was expecting... – Matt Young Apr 29 '16 at 20:54
• xkcd.com/1015 "If you really hate someone, teach them to recognize bad kerning." – MarkU Apr 30 '16 at 7:43

Looks like this is a display artifact of the design of the tabs, interacting with the brower's magnification.

Whichever tab is selected, that tab is rendered with class "youareherre", changing the border-bottom-color to #fff instead of #eaeaea. When viewed at the normal 100% magnification, the white bottom border makes the selected tab look like it is attached to the active page. The gray bottom border of the non-selected tabs is meant to line up with the top border of the active page.

However, when magnification is 90%, the visual elements get slightly misaligned, causing a visible artifact. The normally hidden top border of the questions page, is no longer covered by the header line, and so the non-selected tabs effectively get a thicker 2-pixel line, and the selected tab gets a 1-pixel line. The selected tab's white bottom border is drawn just one pixel above the page's gray border.

This has the effect of making a thicker gray line between the non-selected tabs and the content below.

Stackoverflow.com actually does have the same feature. It looks different when rendered under different magnification.

90% magnification (using chrome browser Version 50.0.2661.94 m):

100% magnification (using chrome browser Version 50.0.2661.94 m):

125% magnification (using chrome browser Version 50.0.2661.94 m):

Personally I think I can live with it. The red top border makes it unambiguous which tab is active.