High lite a text on Specific X&Y Position in Javascript

 
Hi, This is your Invoice No 1234567890

tag. If i want to High lite  dynamically a specific X and Y position of

then how it is possible using pure javascript.Please note  that need only in Javascript not in Jquery. I am not using any-kind of jquery.i f you have any code or idea to do this  then i am really appreciated.
Thank in Advance
KP Singh Chundawat