AdminLTE/scss/dark/bootstrap/_root.scss

:root {
  // Custom variable values only support SassScript inside `#{}`.
  @each $color, $value in $colors-alt {
    --#{$variable-prefix}#{$color}: #{$value};
  }

  @each $color, $value in $theme-colors-alt {
    --#{$variable-prefix}#{$color}: #{$value};
  }

  --#{$variable-prefix}gradient: #{$gradient-alt};
}