Based on Vertex Theme and Material Incognito Dark Theme.
A compiled version of the theme is provided in the release tab. Download the file with the extension .crx from the latest release. After that, drag and drop the file from your file manager to your browser. That should do it.
If you want to tweak and play around with the theme, download the project. Just the manifest.json file and the images folder are really important. To use the theme open a new tab in your browser with the address chrome://extensions and click on Load unpacked extension... and select the directory with the theme files.