Dash to Panel, an icon taskbar for Gnome Shell, was updated to version 20, bringing a window preview overhaul and other improvements.
The Gnome Shell Dash to Panel (not to be confused with Dash to Dock, from which the Ubuntu Dock is forked) extension combines the Dash with the top Gnome panel. The result is a single panel that provides an icon taskbar, the tray, system menu, and date / time indicator. This is similar to the KDE Plasma and Windows 7 (and newer) taskbar. The extension supports Gnome Shell 3.18 and newer.
The latest Dash to Panel v20 includes major improvements to its window previews. With this version, the window previews have been re-written using custom components so they no longer steal input.
Along with this, there are also quite a few new window preview features, like new styling options such as size, padding, close button location, header visibility and font style. And that's not all - the live window previews size is now dynamic for each thumbnail, which makes a lot of sense since windows have different geometries, so previously you'd get huge borders around the previews.
This is how the window previews looked in the previous Dash to Panel versions: