try this,
string mainDiv = "<div> Dear Requestor, </div ><br/><div> Please see below details </div><br/>";
mainDiv+= "<div id = 'divlink' style = '{{divStyleCSSLink}}'> {0} </div>";
mainDiv += "<div id = 'divappend' style = '{{divStyleCSS}}'> {1}" ;
mainDiv += "</div>";
mainDiv += "<br/><br/><br><div> Thank You,<br> ABC </div>";
string final = string.Format(mainDiv, divlink, divtbl);
refer
String.Format Method (System)[
^]