加载在div中的网页不可见，并且无法看到另一个div的滚动条的末尾

In the pasted fiddle link I have 3 div tags in the html section. one div comprises the header part. Second div presents a tree structure and third div loads a webpage. In the result of the fiddle code, 1st div is there with header part. second div is also there with the expected tree structure but could not see the end of the scrollbar. Third div which should show an html page is not showing. In the pasted fiddle link I have 3 div tags in