Glad to hear your reply, DrByte.
It's highlighted in Classic Menu but not in Flyout Menu. I intentionally leave both categories box there so that you can see the difference.

I tried to add following clause to 'categories_ul_generator.php' but didn't work out:
if ($category['current']) {
if ($category['has_submenu']) {
$result .= '<span class="category-subs-parent">' . $category['name'] . '</span>';
} else {
$result .= '<span class="category-subs-selected">' . $category['name'] . '</span>';
}
} else {
$result .= $category['name'];
}

Could you tell me how to make current category bold in the Flyout Menu, same as that in Classic Menu?
Thank you very much.