导航两边是三角形

ul{
            display: flex;
            position: relative;
            &:before{
                content: '';
                position: absolute;
                bottom: 0;
                width: 0;
                height: 0;
                left: -42px;
                border-width: 0px 42px 32px;
                border-style: solid;
                border-color: transparent transparent #000014;
            }
            &:after{
                content: '';
                position: absolute;
                bottom: 0;
                width: 0;
                height: 0;
                right: -42px;
                border-width: 0px 42px 32px;
                border-style: solid;
                border-color: transparent transparent #000014;
           }
}