[Help Wordpress] Fixed width main slide with fill the area mode

I used custom CSS. I feel like I'm getting somewhere. I used this code:

@media screen and (min-width:1026px) and (min-height:1026px) {
  .rsOverflow,
  .rsImg rsMainSlideImage {
      width: 960px !important;
  }
}

However this pushes main slide off centre and adds gap between before and after slides on large screen.

http://www.lakeviewcornwall.co.uk/

Have I picked up the right style item to fix the main slide?

.

help.dimsemenov.com