change the design of 1 Page website with Html- CSS & JS, Add some minor functions as well

I have website A which works flawlessly apart from 1 function that i would like to be added and I have also website B which is build with Pure HTML, CSS and JS but we are taking away the design only from this website B and slamming the design to website A.

If you have this skills and little bit of knowledge about SEO in html + PWA hit me up.

Thanks