Not sure hwo you are styling your gridview. As it's a table I would normally have something along these lines:-
table {
width:90%
}
table td {
font-size:80%;
}
etc.
Now if I want my text underlined in one page only then I would put a class value in the body of the page - <body class="underlinegridtext"> and my style would be:-
body.underlinegridtext table td {
text-decoration:underline;
}