When selecting Azure DevOps Server 2019 on this page, the content doesn't change. However, there is no option to change the UI Theme preference in the place described on the on-prem product.
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Hi @cjwhitsitt, Thanks so much for your feedback. It looks like I need to add some versioning and new screenshots to the content. I've created a user story to capture this work. Thanks again!
Hi @cjwhitsitt, I've just completed a PR, which will go live sometime between today and Monday morning. In the meantime, here's where you go to change the UI theme: Open your profile menu, and then select Theme.

From there you can choose between dark and light. Thanks again for the feedback and have a great weekend!
Might be good to mention that the Theme isn't available till Update 1 of 2019. I know the moniker ranges don't currently support the updates as a version though
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Might be good to mention that the Theme isn't available till Update 1 of 2019. I know the moniker ranges don't currently support the updates as a version though