How to create regex in allow anything content using C# ?

Question

string underlineCss = "'" + "text-decoration: underline;" + "'";
var underlineSpan = @"<span style=" + underlineCss.Replace("'", "\"") + ">(.*?)</span>";
var underlineRegex = new Regex(underlineSpan, RegexOptions.Compiled);
content = underlineRegex.Replace(content, "<u>$1</u>");

Regex  : (.*?)

 

this regex not allow special character and space. so how any content allow in a-z A-z 0-9 special character and space and any other content allow.