.layout {
  display: grid;
    calc( 50vw - 500px )
    repeat( 8, 1fr )
    calc( 50vw - 500px);

This trick means we have an inner grid of 8 columns that is constrained to just 1000px . as the outer gutters are half the size of the screen minus max-screen size / 2 . For some reason the maths checks out!