Follow this post to take a Chrome theme and tweak it to your needs.
Follow How to edit Chrome Themes
Download and install the “just black” theme from the Theme store.
%localappdata%\Google\Chrome\User Data\Default\Extensionsand sort by date modified. Select the first one and find the
Copy the files to another folder, I chose
Change something. I changed
138, 210, 147
Open Chrome and go to
chrome://extension. Enable developer mode (checkbox at the top) and browse to your directory to load your unpacked file
This should load your custom Chrome theme. Continue to tweak as you please.
When you are ready, click the same option to pack your file. This will convert it to a
.crxwhich is the theme file that is portable.