Tag Cloud font size

I have used following code to set tag cloud font size based on each tag’s usage:

add_filter( 'widget_tag_cloud_args', 'all_tag_cloud_widget_parameters' );
function all_tag_cloud_widget_parameters() {
    $args = array(
        'smallest' => 12, 
        'largest' => 28, 
        'unit' => 'pt', 
        'number' => 150,
        'format' => 'flat', 
        'separator' => "\n", 
        'orderby' => 'name', 
        'order' => 'ASC',
        'exclude' => '', 
        'include' => '', 
        'link' => 'view', 
        'taxonomy' => 'post_tag', 
        'post_type' => '', 
        'echo' => false
    );
    return $args;
}

However, the CSS of the theme has following property setting:

.tagcloud a {
    font-size: initial !important;
}

Obviously, the “!important” setting will always override the added filter.
My question: What should be the proper to completely eliminate this font-size setting?
(It is always easy to set a new size in child theme, but it’ll still be constant size and not varied size as per the tag’s usage)

The page I need help with: [log in to see the link]