How to change width of header and site

Does that theme come with a Custom CSS options within the dashboard?
Can you post here the CSS that you’ve tried?

No custom CSS rubrik in the theme.
I changes in a few spots:

#main {
	margin: 0 auto;
	position: relative;
	width: 960px;

#masthead {
	/*display: block;*/
	height: 25px;
	    left: 491px;
	    margin: 1.6em auto 0;
	    padding: 0;
	    position: absolute;
	    top: 130px;
	    width: 960px;
}

#site-footer {
	clear: both;
	color: white;
	font-family:  'almoni-dl', sans-serif;
	font-size: 11px;
	margin-bottom: 30px;
	position: relative;
	padding: 5px 0;
	text-align: center;
	width: 100%;
	width: 960px;
	margin: 0 auto;
}

You should be able to change the width of the site by applying it to the #masthead.

Make sure you make CSS modifications in either a Child Theme stylesheet, or the Jetpack Custom CSS functionality.

It is indeed on the cild theme’s style.css.
Nothing is happening, the main container and sidebar width together, stay 920px. Even when I insert a specific px width to each one of them (that equals together 960px), they stay narrower than the footer, that is the only thing co-operates with me and becomes 960px. (and that after I took it out of the main div).

May you link the problematic webpage?

Ok, I changed the width of the header image in the html (header.php) to 960px and it worked.
Then played forever with the #primary(main) and #secondary (sidebar) and it worked…
Thanks a lot for your time.