css绘制提示框

.level_prompt{
    margin-top: 100px; 
    width:280px; 
    height:80px; 
    position:relative;
    background-color:rgba(1,162,241,0.9); 
    border-radius: 7px; 
}
.arrow{ 
    position:absolute; 
    width:40px; 
    height:40px; 
    bottom:-40px; 
    left:5px; 
}
.arrow *{ 
    display:block;     
    border-width:20px 20px; 
    position:absolute; 
    border-style:solid dashed dashed dashed; 
    font-size:0; 
    line-height:0; 
}
.arrow span{
    border-color:rgba(1,162,241,0.9)  transparent  transparent;
    top:0px; 
    left: 50px;
}