I always need these for my CSS development. They're great for making your CSS more visible for debugging. You can include one or all in your main stylesheet and just apply the style to any div you're working on:

<div class='solid'>Content</div>

.solid { border: 1px solid #000000; }
.dashed { border: 1px dashed #000000; }
.double { border: 1px double #000000; }
.dotted { border: 1px dotted #000000; }
.groove { border: 1px groove #000000; }
.inset { border: 1px inset #000000; }
.outset { border: 1px outset #000000; }
.ridge { border: 1px ridge #000000; }