While looking over the vSphere 8 release notes, I had noticed there was also release notes for new version of the ESXi Embedded Host Client, which is an HTML 5 UI for accessing standalone ESXi host. The really interesting feature that stood out to me was the following:
Ability to change the user interface theme
Initially, I thought this was referring to the new "gray" theme which is the default when logging in.
I thought it was a bit strange to refer to this as being able to change user interface. What I did not realize was that the theme editor for the ESXi Host Client was actually hiding else where in the UI ... Thanks to Mark Gabbs for sharing the details!
UPDATE (10/12/22) - After publishing this blog post, I noticed a more detailed article was posted on the VMware Blog regarding the new ESXi Host Client 2, which includes even more new features such as markdown support for customizing the ESXi DCUI and Host Client login window.