过滤三角形模糊

Question

有没有办法添加隐藏的溢出或类似于实心三角形的东西，所以它仍然显示模糊区域但边缘是实心的？我正在使用这个css，你可以在小提琴中看到 - CancelEdit

.arrow-up {
    border-left: 350px solid transparent;
    border-right: 350px solid transparent;
    border-bottom: 350px solid rgba(0,0,0,0.7);
    position: absolute;
    bottom: -310px;
    filter: blur(7px);
    left: -351px;
}

.arrow-behind {
    border-left: 300px solid transparent;
    border-right: 300px solid transparent;
    border-bottom: 300px solid rgba(0,0,0,0.7);
    position: absolute;
    bottom: 19px;
    left: 49px;
}