Changing the color of the Minimap's visible-area

[fractalf]

https://atom-minimap.github.io/minimap/

atom-text-editor atom-text-editor-minimap::shadow .minimap-visible-area,
atom-text-editor::shadow atom-text-editor-minimap::shadow .minimap-visible-area {
  background-color: green;
  opacity: .5;
}

^ that didn't work for me

this however did:

atom-text-editor atom-text-editor-minimap .minimap-visible-area::after {
    background-color: #649de0;
    opacity: .3;
}