CRM forms use lots of stylesheets to design their forms. It can be a very tough job to be able to design a custom form with the same look as that of standard CRM Forms. IE developer tool can be of great help in getting you closer to be being able to design similar looking forms.
The tool is made available by Microsoft and it help you to review the properties and stylesheet of specific element of the pages being displayed in your IE browser.
Once you install the tool it would be available on the IE standard toolbar as shown below.
Clicking on this button will show up the tool IDE with all the information. It is more organized way of what we get after view source.
If need to know properties (id/stylesheet info) of any field, area, left nav on form then choose select element option