You can select any object on the design-surface and then click on the "properties" panel on the right-hand side of the screen to customize its properties:

Figure 9

Above I'm changing the "Background" brush of the button to be a deeper blue gradient (the third tab circled in red under the "Brushes" node allows us to configure the gradient brush). 

Useful Tip: The properties window includes a search box near the top that you can optionally use to filter the visible property names:

Figure 10

Because all UI objects in Silverlight and WPF are composed using vector graphics, we can shape/stylize/transform controls however we want.  For example, we could either set the "Transform" properties on our Button control or click on the corner edges of it to rotate/skew/scale it:

Figure 11

This gives us a lot of power and flexibility to quickly and easily customize the experience however we want:

Figure 12

Useful Tip: You can zoom in and out of the design surface by holding down the ctrl key and then use the wheel of your mouse to control the zoom depth.  You can then move the viewable region of the design surface by holding down the space bar, which will cause a hand-cursor to display, and then you can hold down the mouse and use it to drag the currently visible region around the screen.  This later tip is useful when you are zoomed way in and want to easily move the visible content around.