my c# code not accepting rotate style

Question

  watermarkContent = "Viewed by " + dsUserDetails.Tables[0].Rows[0]["ContactFirstName"].ToString() + " " + dsUserDetails.Tables[0].Rows[0]["ContactLastName"].ToString() + " " + dsUserDetails.Tables[0].Rows[0]["OrgTimeZone"].ToString();

 

strBody.Append("<span style='transform: rotate(-90deg);color: #7a7a7c;font-size: 13px;font-family: Arial;line-height: 30px;margin:0 15px 0 0;padding:0;'>" + watermarkContent + "");

 

this is my code . here i apply  rotate but it is not apply . please help to me.

 

I attached my image