To get complete dark theme you must use IDASkins and Ida Consonance
If you're using IDA 6.5 - > 6.9 you will need IDASkins 1.4.1
For all versions of IDA you can use the same ida-consonance version for the code blocks and highlighting.
Install IDASkins first:
Copy IDASkins.p64 & IDASkins.plw into the IDA plugins folder
Open IDA Pro
Edit -> Plugins -> ...