border制作三角形

border制作三角形

.arrow-up {
    width: 0;
    height: 0;
    border-left: 5px solid transparent;
    border-right: 5px solid transparent;

    border-bottom: 5px solid black;
}
.arrow-down {
    width: 0;
    height: 0;
    border-left: 20px solid transparent;
    border-right: 20px solid transparent;

    border-top: 20px solid #f00;
}
.arrow-left {
    width: 0;
    height: 0;
    border-top: 10px solid transparent;
    border-bottom: 10px solid transparent; 

    border-right:10px solid blue;
}
.arrow-right {
    width: 0;
    height: 0;
    border-top: 30px solid transparent;
    border-bottom: 30px solid transparent;

    border-left: 30px solid green;
}