This is a fork of jasperro's FlatColor 2.0 Gtk-theme (original readme below) that has been refactored to get its colors from a single base16-compatible css file. Also, a wrapper was added to package the theme as a Flatpak.
This is a updated version of FlatColor by deviantfero, with rounded corners, some fixes and shadows. It was made to be hackable and simple. The colors can easily be changed by programs like wpgtk and pywal.
This theme has a old version of the gtk3.0 theme, it should only be used as fallback. Gtk3.20+ have full support.
The theme looks similar to vimix/adapta.