So broader CSS colors and theming changes can be done with a bootstrap 4 template (we have people who have worked on upgrading to bootstrap 5 but that work is not complete right now). That’s how the 40+ themes in OpenEMR are currently handled. They are all a compilation of a bootstrap 4 theme.
However, trying to make broad, consistent structural changes are going to require the work of a developer, and most likely a good one at that due to OpenEMR’s sprawling codebase with many different design patterns used. It wouldn’t make sense to hire a designer w/o also coupling that with a developer who knows the codebase well.
Its much easier to design and build a single page, such as a dashboard (and I say that with some caveats as it depends on how complicated the dashboard is), then it is to try and apply a large structural change to all the pages in the site due to how fragmented the OpenEMR page architecture is. It can definitely be done, but will require a lot of work. I imagine @visolveemr knows a whole lot about the pain points involved in this as they’ve been around for a long time in the community (great to hear from you again BTW).