This week Azure DevOps finally rolled out one of their most requested feature, a dark theme. I use dark theme for just about any app that supports it, so this is a welcome addition to Azure DevOps. Keep in mind that this is just a preview and is still being refined.
To switch to Dark theme, go to your Azure DevOps portal and click on your user dropdown menu in the top right corner. Them click on Theme menu item.
The theme options pane will then be displayed. Click on the Dark (preview) option to switch to the dark theme.
Voila! DevOps in Dark theme.
Switching to dark theme is a personal choice and is not something that is forced across your organization, which is nice. I recommend you give it a try and see for yourself.