Here the System-Monitor-Sidebar.png with Christmas Look.
In the zip file are 4 png's each with other Look.
Change when you do the Follow_
When you have Download it,then go with admin rights to the folder /usr/share/pixmaps/gnome-system-monitor/side.png
i have rename the original side.png in 1side.png and i have renamed the side-solus4.png in side.png that was all
This original side.png was make from
SolusOS Member archangelse7en.
I have change it with a Christmas Outfit.