function styleActiveDropZones(dropZones, getStyles = () => {}, getClasses = () => []) {
    dropZones.forEach(dz => {
        const styles = getStyles(dz);
        Object.keys(styles).forEach(style => {
            dz.style[style] = styles[style];
        });
        getClasses(dz).forEach(c => dz.classList.add(c));
    });
}
will mark the given dropzones as visually active
@param {Array<HTMLElement>} dropZones
@param {Function} getStyles - maps a dropzone to a styles object (so the styles can be removed)
@param {Function} getClasses - maps a dropzone to a classList