css
.border-up{
position: relative;
width: 0;
height: 0;
/*向上*/
/*border-width: 0 30px 30px;*/
/*向下*/
/*border-width: 30px 30px 0;*/
/*向左*/
/*border-width: 30px 30px 30px 0;*/
/*向右*/
border-width: 30px 0 30px 30px;
border-style: solid;
/*向上*/
/*border-color: transparent transparent #333; */
/*向下*/
/*border-color: #333 transparent transparent ;*/
/*向左*/
/*border-color: transparent #333 transparent transparent;*/
/*向右*/
border-color: transparent transparent transparent #333;
margin: 48px auto;
/* 全透明黑色 border-color*/
}
.border-up span{
display: block;
width: 0;
height: 0;
/*向上*/
/*border-width: 0 28px 28px;*/
/*向下*/
/*border-width: 30px 30px 0;*/
/*向左*/
/*border-width: 30px 30px 30px 0;*/
/*向右*/
border-width: 30px 0 30px 30px;
border-style: solid;
border-color: transparent transparent #ff0;
position: absolute;
top: 0;
left: -28px;
}
.popup{
position: relative;
width: 200px;
height: 50px;
background: #f08;
margin: 300px auto;
}
.popup span{
border-width: 0 30px 30px;
border-color: transparent transparent #f08;
position: absolute;
top: -30px;
width: 0;
height: 0;
border-style: solid;
display: block;
}
demo
<!-- 带边框的三角形 -->
<div class='border-up'>
<span></span>
</div>
<!-- 气泡的三角形 -->
<div class="popup">
<span><em></em></span>
XXXXXX
</div>