Take a look at rogerdudler/eclipse-ui-themes . In the readme there is a link to a file that you need to extract into your eclipse/dropins folder.
When you have done that go to
Window -> Preferences -> General -> Appearance
And change the theme from GTK (or what ever it is currently) to Dark Juno (or Dark).
That will change the UI to a nice dark theme but to get the complete look and feel you can get the Eclipse Color Theme plugin from eclipsecolorthemes.org. The easiest way is to add this update URI to “Help -> Install New Software” and install it from there.
Eclipse Color Themes
This adds a “Color Theme” menu item under
Window -> Preferences -> Appearance
Where you can select from a large range of editor themes. My preferred one to use with PyDev is Wombat. For Java Solarized Dark