Via css. Put this inside the <head> tag.
<style type="text/css" media="screen">
table{
border-collapse:collapse;
border:1px solid #FF0000;
}
table td{
border:1px solid #FF0000;
}
</style>
For internal gridlines, use the tag: td For external gridlines, use the tag: table
<table border="1"></table>
should do the trick.
Source: Stackoverflow.com