[Theme Horse Support Team]

Hi LMKWeb
Though you set the wide or narrow layout the menu will cover the 978px and it will be center aligned. We have designed the theme that way.
2. For the wide layout the background will be ineffective as the content are will cover the whole width. The background will only be used if narrow layout is selected.
3. In our demo we are using the narrow layout.

the default size for narrow layout and wide layout is this

add_image_size( 'slider-narrow', 1038, 460, true ); 		// used on Featured Slider on Homepage Header for narrow layout
add_image_size( 'slider-wide', 1400, 460, true );  

it is inside attitude-> functions.php

Regards
Sunil