For a soft, almost creamy look on the Xfce desktop, the Theme “Victory” by newhoa is the ideal choice. It consists of 5 variants in different brightness levels for windows and window frames, as well as an extensive icon set. Installation is very simple:
As a regular user, you clone the corresponding git repository and store the data in your user directory under .icons or .themes.
git clone https://github.com/newhoa/victory-icon-theme.git ~/.icons/victory-icon-theme/
git clone https://github.com/newhoa/victory-gtk-theme.git ~/.themes/
The theme can then be activated under Settings → appearance. In the same window there is also a tab for Symbols. To select the appropriate window frames, go to Settings → Window management. Of course, the changes can also be combined in different ways and reversed in the same way. Oh, and a theme variant for HiDPI displays is also included!