The problem in the code that you originally posted is that you have not configured the page correctly for the splitter (or any HTML element) to occupy 100% of the height of the page. However, you mention that you have added height for the HTML, BODY and FORM elements. You actually have to set the height for the DIV with id="mainpage" as well, because it is a parent of the splitter as well. As soon as I configured those elements, the splitter became as high as the viewport of the browser:
|html, body, form,
| height: 100%;
| padding: 0px;
| margin: 0px;
At this point, you get scrollbars because you have not only a splitter, but text above the splitter as well, which has a height of its own. Please review our Making RadSplitter occupy part of a page with variable size
online article. Please note that in order to get the expected result, you have to remove the following DIV element, as it does not have a HeightOffset property:
|<div style="border: solid 1px #00ff00; height:100%; margin: 0px; padding: 0px;
I would also recommend that you update your version to the latest version of the RadControls for ASP.NET AJAX suite (2008.3 1314.35), as I noticed that you use an old version - 2008.2.826.35.
the Telerik team
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