Reset CSS

For reset CSS need to add default css for each tags,

e.g. body,div,h1,h2,h3,h4,h5,h6,pre,input,p,th,td
{
margin:0; padding:0;
}

Here reset div tag and input tag parameters(margin and Padding), Same way you need to reset all styles for each tag.

Disable back button of Browser

Add this code in Master page or page for disable browse back button.

Page.Response.Cache.SetCacheability(HttpCacheability.NoCache);
Page.Response.Cache.SetNoStore();
Page.Response.Expires = 0;

In this case browser not cache you page and each time when you click back button request goes to server and get response from server.