How can I close this gap using CSS?

you seem to have copied some excess codes into your new section:

try to remove those lines from the <!--Alex--> section:

<div class="wrap wide">
    <header id="header">
        <!--<div id="logo">
			<!--<h1>
			<a href="http://www.diylikethetrade.co.uk" title="DIY Like the Trade">
				DIY Like the Trade			</a>

			</h1>-->
		</div><!-- / #logo -->

untested – if this does not work, please contact the theme’s developer for support.

this forum only supports themes from http://ww.wp.xz.cn/themes/