Custom themes not working after portal upgrade 7.5

Hi,

We have upgraded our portal from 7.3 to 7.5. In WDABAP iViews the url text colors and images are changed. We think this is due to custom themes.

1. We have UI theme designer now in 7.5 and no theme editor In NWA, already we have blank in the property Determine what will be the theme runtime provider, but we are unable to see the Theme Editor. https://archive.sap.com/discussions/thread/3755478

2. We have taken backup before upgarde and have to use our custom theme which was developed in 7.3 How to resolve the issue?

Please guide us as we have checked below blog, not not clear for us on .CSS or .LESS https://blogs.sap.com/2014/04/01/how-to-ui-theme-designer-migration/

Is the CSS checks required in our case?

Thanks & Regards,

Prasad