A customizable framework to add 2 pages onto an active website

Our aim is to run a theme based campaign for our website audience for a duration of 12 months; May 2019 to April 2020.
2 themes will be covered each month i.e. 24 themes in total.
Only one theme will be run at a time, ideally scrapping the previous theme to make room for the new one. We require a single framework, which allows us to replace images & written content of the current theme with the subsequent themes.
The PPTs attached have the wireframe & the sample design.
The user should be able to transition between the 2 pages & the pages must be responsive & browser neutral.