Hero video is too large – how can I reduce video size? + Nav menus in Widgets

Hi I have a video header which is working fine on the website but it is too large. It was built with Content Samurai and they say that the size should be able to be adjusted in the theme but I can't seem to find where or how. Also it does not work on mobile at all. I have therefore put a static header. Is there any reason it won't work on mobile? The sidebar I have created for my front page has nav menus. The spacing is awful and I would like to reduce it. Please could you give me the css to do this? site is at http://cassowarycoastlife.com.au Any help would be appreciated. Thanks