css如何创造出三角形

/* Sub menu indicators

===================*/

.sm-blue a span.sub-arrow {

position:absolute;

bottom:2px;

left:50%;

margin-left:-5px;

/* we will use one-side border to create a triangle so that we don't use a real background image, of course, you can use a real image if you like too */

width:0;

height:0;

overflow:hidden;

border-width:5px; /* tweak size of the arrow */

/*border-style:solid dashed dashed dashed;

border-color:#a4cde1 transparent transparent transparent;*/

border-style:dashed dashed dashed dashed;

border-color:transparent transparent transparent transparent;

}

.sm-blue-vertical a span.sub-arrow,

.sm-blue ul a span.sub-arrow {

bottom:auto;

top:50%;

margin-top:-5px;

right:15px;

left:auto;

margin-left:0;

border-style:dashed dashed dashed solid;

border-color:transparent transparent transparent #a4cde1;

}