A new version of leaked Skype UWP preview app has been released. The current version is 188.8.131.52, which is only available for Windows 10 Mobile Redstone branch.
The new Skype is better in terms of design and performance and the dark mode looks pretty good. However, its a leaked version, so you can expect some odd elements and the bugs.
Note: The easiest way to download the app is via browsing on a PC. Download it through the link given below on your PC and transfer it to your phone and just tap on Install button. Before downloading the appxbundle, go to Settings -> Update & Security -> For developers and enable Developer mode.