This theme is a very small pack of a light theme and dark theme with darkest background with monokai syntax highlighting.
To change background and syntax colors manually follow steps given below:
Settings > Workbench > Appearance
On right side panel, Click on "Edit in settings.json" under Color Customizations.
Just paste the below code:
You will see sidebar and activity bar color changed.
For more you can visit "https://code.visualstudio.com/api/extension-guides/color-theme".
To create your own custom theme, you can refer the above link as well.