How to reverse color of child elements mix-blend-mode?

Question

When I use "mix-blend-mode" for an element, but I want the span of the element to not be discolored? So is there any solution?

a {
    width: 160px;
    height: 160px;
    margin: 0 auto;
    border-radius: 100%;
    background-color: #000;
    mix-blend-mode: exclusion;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #fff;
    padding-top: 5px;
    font-size: 16px;
    position: relative;
    top: 0;
    transition: .2s linear;
    font-weight: bold;
}
span{
   position: relative;
   z-index: 1;
}

I tried:

a{
>!  background-color: #000;
>!  mix-blend-mode: exclusion;
}
a:before {
  position: absolute;
  content: '';
  width: 100%;
  height: 100%;
  background-color: #000;
  mix-blend-mode: exclusion;
  filter: invert(1);
  z-index: -1;
}