Ah ok, I hadn't noticed that had been updated, but  _dimensions has $gutter-one-sixth that _measurements.scss doesn't have. Also _dimensions also contains $max-site-width: 960px;

I will have a look at updating the css so I can remove _dimensions i.e. update  $gutter-one-sixth to use $gutter-one-quarter and move or remove $max-site-width: 960px; if superfluous.

https://github.com/alphagov/hmrc-contacts/blob/master/app/assets/stylesheets/frontend/styleguide/_dimensions.scss