keeweb/app/styles/base/_theme-vars-support.scss

@function text-contrast-color($bg, $lshift, $th-bg, $th-text) {
    @if (lightness($bg) - $lshift >= lightness($th-bg)) {
        @return $th-text;
    }
    @return $th-bg;
}

@function lightness-alpha($color, $lightness, $alpha) {
    @return adjust_color($color, $lightness: $lightness, $alpha: $alpha);
}

@function semi-mute-percent($percent) {
    @return $percent / 2;
}