Web Forms :: Find Exact Word In Text File?

I have style.css file, which is edited programatically. I look for css classname in file and update css file accordingly.

But I am not able to find index of exact word in css file. Ex. I am looking for "body a:link" in css file but it gives me index of ".cp-body a:link"

Here is sample content of style.css which I read into string varible "strStyle"

.cp-body a:link
{
color: #FF0000;text-decoration: none;
}
body a:link
{
color: #CCFF33;text-decoration: none;
}

Here is code to find index of exact word:

string cssClassName = "body a:link";
string regexPattern = string.Format(@"{0}", cssClassName);
Regex rx = new Regex(regexPattern);
int sPos = -1;
if (rx.Match(strStyle).Success)
{
sPos = rx.Match(strStyle).Index; //strStyle is css file content
}

I have used  in regular expression to find exact word, but still I am getting index of ".cp-body a:link",

instead it should give me index of "body a:link"