Removed menu but white shade remains

start by creating a child theme to work with – do not edit the default theme Twenty Eleven directly. https://codex.www.ads-software.com/Child_Themes

in header.php remove this full section:

<header id="branding" role="banner">

			<nav id="access" role="navigation">
...
...
			</nav><!-- #access -->
	</header><!-- #branding -->

make a backup copy in case you need to reverse the edit.

Thank you.