Relocate the search css to the end in header.css

This PR only relocates search in header.css to the end.

Before it was somewhere in the middle. If you use the file as template, it is easier to have search collected at the end to comment it out if necessary (like when using an own css/setup). This also makes updating more easily when deriving from the default.

Bundling with gulp bundle runs fine, gulp preview is also without issues.

I came across this when realigning our UI to the default UI for ease of maintenance.