This has nothing to do with PHP. PHP has no control over how things are displayed on the client side -- all PHP can do is print the HTML and CSS that changes how it looks on the client side.
That said, the best CSS reference you'll find is the one at w3schools
, but here's the gist:
<style type="text/css" media="screen">
border: 1px dotted blue;
Btw, IE/Win is stupid and displays "dotted" borders like "dashed" ones. Mozilla/Firefox get it right, as do (I think) current versions of Opera and Safari.