如何在Wordpress中使用类别slug url？

I'm in designing a WP Theme. I need help! I'm calling category and it's slug from plugin functions. Here is the code:

$category = get_the_category();
$html .= '<div id="category-post" class="category-main category'. $category[0]->slug .'">';
$html .= $category[0]->cat_name;
$html .= '</div>';

Let's say I have a class name for health category: .category-health

but the above code will returned to: <div id="category-post" class="category-main categoryhealth"></div> and the class: .category-health not working because it returned to unavailable category: .categoryhealth

From above code I feel that the category slug " - " is not working. Because the right class is ".category-health" and not ".categoryhealth"

Is there any way to fix this? Thanks

Maybe it will help some one else with this answer. The right code is:

$category = get_the_category();
$html .= '<div id="category-post" class="category-main category-'. $category[0]->slug .'">';
$html .= $category[0]->cat_name;
$html .= '</div>';

I just add - after category, category-main category–. almost like Nilambar said.