CSS and Java optimization + tracking code for GA for visitors redirected to whatsapp (floating widget)

I would like to optimize CSS and JS code to accelerte website speed in wordpress. eg. style.min.css file. Development envirnoment available to test first. Also, i would like to create a tracking code (snipet) to capture and track in Google Analytics the redirected website traffic to whatsapp (when a user on the website clicks on the whatsapp floating widget)