Admin > Customise > Select the current theme > Edit CSS/HTML > Paste that into the CSS section.
The 10px and 3px control the size of the glow and the #f00 is the colour.
Admin > Customise > Select the current theme > Edit CSS/HTML > Paste that into the CSS section.
The 10px and 3px control the size of the glow and the #f00 is the colour.