To set letter spacing with CSS, use the em measurement unit.
A relative measurement of the height of a font is em spaces. Because an em unit is equivalent to the size of a given font, if you assign a font to 12pt, each "em" unit would be 12pt; thus, 2em would be 24pt.
You can try to run the following code to use CSS to set letter spacing:
<html> <head> </head> <body> <div style = "position:relative;left:90px;top:3px;background-color:yellow;letter-spacing: 2em;"> This div has relative positioning. </div> </body> </html>