分辨各种浏览器的hack

/* Opera */
html:first-child #opera
{
display: block;
}
/* IE 7 */
html > body #ie7
{
*display: block;
}
/* IE 6 */
body #ie6
{
_display: block;
}
/* Firefox 1 - 2 */
body:empty #firefox12
{
display: block;
}
/* Firefox */
@-moz-document url-prefix()
{
#firefox { display: block; }
}
/* Safari */
@media screen and (-webkit-min-device-pixel-ratio:0)
{
#safari { display: block; }
}
/* Opera */
@media all and (-webkit-min-device-pixel-ratio:10000), not all and (-webkit-min-device-pixel-ratio:0)
{
head~body #opera { display: block; }
}