Customize the appearance of Windows Sidebar

Windows Sidebar Styler is an application designed to allow users to tweak the Sidebar’s User Interface.
Custom styles allow users to customize the appearance of Windows Sidebar so that it fits the style of other UI elements, such as the Aero Glass colorization or third party themes.
You can save your visual styles and share them with other users.
Windows Sidebar Styler also adds support for WPF Gadgets; Gadgets now take full advantage of Windows Presentation Foundation - a powerful managed code-oriented framework for presenting rich visual compositions such as vector graphics, 3D drawing, animations and more.
Original: Image Minimalistic Style: Image
The visual styles below remove the grey Panel background, the "Add Gadgets" button + the Close, Config & the Gripper buttons that appear when you hover over the Gadgets (see image above). You can still access these functions in the right click menu from the Sidebar & Gadgets. The MinimalistiClear Style also removes the backgrounds.