Re-code 2 static html pages so that they incorporate a responsive design

The pages that I need to be re-coded are:

https://www.onlywhat.com/uk/default.htm
https://www.onlywhat.com/uk/get-quotes-from-accountants.htm

The requirement is to be able to present the same pages on various devices (desktop as shown, tablet, phone) I will be using both as templates for new pages.

Deliverables:
default.htm, amended style.css
get-quotes-from-accountants.htm, amended style.css

I will test both pages on desktop, tablet and phone devices using standard browsers and different browser window sizes.

All files will be provided (htm,css,js)