Css style in asp.net

Css style in asp.net

<style type="text/css">
.style1
{
border:2px solid #e53a6f;
box-shadow:0 0 5px 0 #e53a6f;
}
</style>
javascript
<script type="text/javascript" language="javascript">
if (Pname == "")
{
document.getElementById('<%=txtname.ClientID %>').style.border="2px
solid #e53a6f";
return false;
}
</script>
I am new to css. My question is I want to call style1 css instead of
calling .style.border="2px solid #e53a6f";in java script . Is this
possible?. Can some one help me out.