Uyuni/SUSE Manager build client tools for each of the supported operating systems: SLES 11, SLES 12, SLES 15, RHEL 6, RHEL 7, RHEL 8, Ubuntu 16.04, Ubuntu 18.04, Ubuntu 20.04, Debian 9, Debian 10... the list is long. This is required because each operating system has different base libraries (glibc, OpenSSL, Python version, etc).
A few months ago, the SUSE Manager development team started a (yet unfinished) research task to try to build Salt and all the required dependencies (minus glibc and OpenSSL, because it would break FIPS certification) so that we can always ship the latest version of Salt on each client operating system:
Currently, Uyuni has three themes: Uyuni, SUMA light & SUMA dark. All of these are tailored around a common core using CSS preprocessor variables, mainly to switch out colors, fonts and the like. Core layout such as spacing, sizing and so forth is shared between all three and stems from the shared core.
At the moment, Uyuni uses a pretty standard frontend build chain based on Webpack 4, Terser, and a few loaders here and there. This works reliably, albeit fairly slowly. In part this may be attributed to large package sizes, in part to the tooling itself.