Rambox-CE/ext/packages/ext-theme-base/sass/etc/mixins/theme-background-image.scss

/*
 * Method which inserts a full background-image property for a theme image.
 * It checks if the file exists and if it doesn't, it'll throw an error.
 * By default it will not include the background-image property if it is not found,
 * but this can be changed by changing the default value of $include-missing-images to
 * be true.
 */
@function theme-background-image($path, $extension: $image-extension, $nocheck: false) {
    $path: file_join($relative-image-path-for-uis, $path + '.' + $extension);
    $background-image: none;

    @if $path {
        @if $nocheck {
            $background-image: $path;
        } @else if theme_image_exists($image-search-path, $path) {
            $background-image: $path;
        } @else {
            @warn "@theme-background-image: Theme image not found: #{$path}";
            @if $include-missing-images {
                $background-image: $path;
            }
        }

        @if $background-image != none {
            $background-image: url(file_join($theme-resource-path, $path));
        }
    } @else {
        @warn "@theme-background-image: No arguments passed";
    }

    @return $background-image;
}