Splitter is nested into a layer with
height set to
500px and
width set to
700px.
Splitter
Width and
Height properties are set to 100% to fill the entire layer size.
Source Code & Description
Fill Container Size
If you place the RadSplitter into a container element in the page you can set its Width and Height properties to 100% and this will resize the splitter to fill the dimensions of the container element. You should set all the panes dimensions in % as well.