Trouble displaying the tagline

Hi,
I am trying to display the tagline on my site and was able to do so by inserting this code into my header.php.
<?php bloginfo( 'description'); ?>

But I can’t get the css to affect it, so I think I may have placed the code in the wrong place, but if I put it within the <title> tag it doesn’t show. I am using a theme that allows for a custom logo, which is in place, but it then turns off the title and tagline.

I would like to use the tagline as well as the custom logo and have it appear under the nav buttons.

https://marketsindevelopment.com

I am new to php and trying to understand it – any help would be much appreciated.