CSS Parallax expert needed

I have a simple but fully CSS Parallax script. I need some adjustments: The document has several parallax segments. structure is as following: 1. startscreen segment: parallax back layer and base layer 2. content segment: only base layer 3. sub header segment: parallax back layer and base layer 4. content segment: only base layer 5. sub header segment: parallax back layer and base layer 6. content segment: only base layer 7. sub header segment: parallax back layer and base layer 8. content segment: only base layer All segments are currently based on viewport height (vh 100). However there is need to change without to destruct the whole parallex set and appearance. The startscreen segment (1.) need to remain at viewprt height. The subheader segments (3.,5.,7.) need to set on a height of 600px. Moreover it need to be adjustable without interfering to the rest of the design if the requirement changes. The content segments (2.,4.,6.) will contain dynamic content. so the height of the segments will be different from each use case and viewport size (responsivity) Currently it is not possible to adjust heights without destruct the other segments and the whole website geometry. This need to be changed / reconstructed to grant consistent design at all applications. The code shall be realized ONLY in HTML and CSS. No JS ! Please work clean, modular and make the code easy reusable.