I am having a long drop down menu .I have used the overflow property by which it is getting scrolled....But it does not look nice...Please suggest me how to give good CSS to scrollbars
In modern browsers you can only use proprietary css properties to style the scroll bar. Here is a link to the -webkit properties available: http://css-tricks.com/custom-scrollbars-in-webkit/
If you want a more cross-browser solution, you're going to have to use some JS. Here's a plugin that I've used before that works fairly well and is easily customizable: http://www.dynamicdrive.com/dynamicindex11/facescroll/index.htm It works like the scroll bars on Facebook and works extremely well for dropdown menu scenarios.