First, dark theme download from This page.
Follow, unzip the package you downloaded. Inside, you will find lots of files with names like “filetypes.python” and “filetypes.html.” Now just copy and paste the files in ~ / .geany / filedefs /
As Geany version 0.16, paste the file into the ~ / .config / Geany / filedefs /
You can copy / paste all these files to perform everything you open, or selected files, said filetypes.html to perform only html files.
The next time you start Geany, you will have a dark master

Also you can bamboomat Click here to self customize according to their own wish.