Fork of the theme Simple White by Louis Chan for Pale Moon with elements ported from Simple White X.
Simply download the contents of the "src" folder and pack the contents into a .zip file. Then, rename the file to .xpi and drag into the browser.
On Unix systems (or Windows 10, with WSL) you can optionally run build.sh instead. Running this as-is will produce a .xpi file ending in -dev, and if run from the command line and appending a number (e.g. ./build.sh 2) will append that number to the filename instead.
You can grab the latest release either from the Releases section of this repository, or the Pale Moon Add-Ons Site.