Yes our theme is responsive but it seems that you have kept the banner image in wrong way, so please follow the following steps to fix the banner issue;
Go to Dashboard => Appearance => Widget => Banner Wide => And keep the text widget inside the banner wide widget and keep your image in text widget in content area but you need to use like this code to keep the image
Then save it.
And it seems that your menu css is overwriting by other css, so please use the following css to fix your issue;
NOTE: Please use the child theme style.css or custom css plugin to write the css