Why is my search button glitching in Dawn 12.0?

[imandco]

Hello. The search button in my header isn't working properly. When I scroll the page and then click search in the header it just blinks and glitches. It works better sometimes than others. The video shows the problem, the first glitch happens at 00.21 sec. 

Video link: https://www.awesomescreenshot.com/video/24692261?key=de6c47cc3f9288f3c235643c44ff3737

Website: www.inhabitmarket.com

Please let me know how to fix this. 

Thanks in advance!