How can I remove the space between the header & the browser’s navigation bar?

Indeed, I want my header to touch the browser’s nav bar.
I use mandigo theme and been tryng a few tricks such as:

* Following the advise on the thread on https://www.ads-software.com/support/topic/169780
and looked for the “container” or “nav” padding or margin but didn’t find any similar code to edit…

edited
margin-top: <?php echo ($mandigo_options['header_blogname_smaller_font'] ? 25 : 15); ?>px;

Changin the 25 and 15 value to 0, but it didn’t work either..,

I would greatly appreciate help!

NB: Mandigo theme states on “style.css”
The rules below are not used, they are here for www.ads-software.com to accept the theme upload. The actual stylesheet is style.css.php