How to combine map keys into a ruleset in SCSS?

Question

Sass

Hello, I have a map with data like this:

$rank: (
   [8, 7]: red,
   [6, 5]: blue,
   [4, 3]: green,
   [2, 1]: black,
);

I need to get a set of rules like this:

.rank--8, .rank--7 {
   color: red;
}
.rank--6, .rank--5 {
   color: blue;
}
.rank--4, .rank--3 {
   color: green;
}
.rank--2, .rank--1 {
   color: black;
}

So far, nothing better than this has come up:

.rank {
   @each $level, $color in $rank{
      @each $level_val in $level {
         &--#{$level_val} {
            color: $color;
         }
      }
   }
}

But this is not quite what you need, the result is like this:

.rank--8 {
   color: red;
}
.rank--7 {
   color: red;
}
.rank--6 {
   color: blue;
}
.rank--5 {
   color: blue;
}
.rank--4 {
   color: green;
}
.rank--3 {
   color: green;
}
.rank--2 {
   color: black;
}
.rank--1 {
   color: black;
}

How can you achieve the desired result?