style hr

hr{border:none}

在firebug下面看會是 hr{border: medium none}，border-width: medium 是 border 的 default setting，可以參考 blueprint 的 demo page
Styling <hr> with CSS

Various CSS properties can be applied on <hr>:

* All three browsers allow setting width and height of the <hr> element.
* The border property can be used in IE and Mozilla. It does not work well in Opera (see examples below).
* <span style="font-weight:bold;">IE uses the color property for the <hr> element.</span>
* <span style="font-weight:bold;">Opera and Mozilla use background-color for the <hr> element.</span>
* All three browser allow setting a background-image of the <hr> element, however this is not very useful in IE and Opera (see the last example).