According to the internal changelog attached at the end of the article, GTK+ 3.19.7 adds support for kinetic scrolling, drag cancellation and DND (Drag-and-Drop) actions on Wayland, adds a brand new managed Drag-and-Drop functionality for both X11 and Wayland, fixes numerous issues for the Adwaita theme, and tries to provide partial control over cursor blinking for GtkTextView.
Moreover, GTK+ 3.19.7 ships with several CSS changes, among which we can mention the addition of support for CSS names to even more GTK widgets, support for recoloring icons with the -gtk-recolor option, and a fix for an issue with the rendering of asymmetric borders. The GtkNotebook widget has been updated to use gadgets and to no longer use style properties. Also, GTK+ 3.19.7 further improves the GTK+ widget drawing scalability, especially for containers that have multiple children, such as huge flow or list boxes.
Numerous bugs have been fixed in GTK+ 3.19.7
Last but not least, the new milestone of the upcoming GTK+ 3.20 GUI toolkit fixes numerous bugs that have been reported by users or discovered by the hard-working development team since the previous release of the software, and updates several language translations, among which we can mention Brazilian Portuguese, Japanese, Finnish, and Slovak.