A custom header area request

`I would like to have a somewhat thick black bar extend across the full width of my website, directly below my main menu items.

Consider this;

[Logo and background image]
[Global Twinning] [Forums] [Etc]
[Black bar begins- no white space gap, begins immediately after the menu ends]

The reason i am interested in having this, is because it would give a feeling of separation between the main menu and the white space below, the white space below that exists as padding for all the other pages of the website.

These custom-abilities make the website look highly customized and classy.
To clarify any confusions, I would like for there to be a black bar that extends across the full width of my website, directly below the main menu items; where the background image ends.
Consider it like; “the blue ends, the black line begins”

This website is a reference point http://www.scmjf.org/