#triangle-up {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
}

#triangle-down {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid red;
}

#triangle-left {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-right: 100px solid red;
border-bottom: 50px solid transparent;
}

#triangle-right {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-left: 100px solid red;
border-bottom: 50px solid transparent;
}

#triangle-topleft {
width: 0;
height: 0;
border-top: 100px solid red;
border-right: 100px solid transparent;
}

#triangle-topright {
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 100px solid transparent;
}
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 100px solid transparent;
}

#triangle-bottomleft {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-right: 100px solid transparent;
}

#triangle-bottomleft {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-right: 100px solid transparent;
}
css3 实现圆角的三角形
background: linear-gradient(45deg, transparent 50%, #61C4CF 0%);
background-size: 16px 16px;
border-top-right-radius: 3px;
