https://www.youtube.com/watch?v=MEzCfNIZSW4

theme builder needs installing via plugins

It will only modify how next experience UI looks, it will not modify legacy UI16 look

navigate to it via:

https://.service-now.com/now/theme-builder/home

currently does not change branding across portals but it should be a long term goal

note the paragraph on /now/theme-builder/edit-overview/8d16b1ce97e66110df843a300153af52

Currently, you need to update system properties to use your logo. See details.Link opens in new window or tab We’re working to make this simpler for you.

which takes you to a docs link: https://docs.servicenow.com/bundle/utah-platform-user-interface/page/administer/navigation-and-ui/task/tb-upload-logo.html

this shows you which sys property to set up in order to enable theme builder to override your logo > Ensure that the glide.ui.polaris.theme_builder.override_logo system property is set to True.

Only Polaris has a Dark Variant as of v1 but something that will be looked at in future for other themes