Consider following:
... .box{ width:500px; border-bottom: 1px solid #ccc; }
It will set the bot
You could use a background-image:
.box{ width:500px; border-bottom: 1px solid #ccc; background-image:(yourimage.png); /*make your image a solid line 1px tall by 250px wide (or so)*/ background-position: bottom left; background-repeat:no-repeat; }