Add contain-float mixin; fix other cruft changes
Add contain-float mixin; fix other cruft changes

bitzesty/trade-tariff-frontend,bitzesty/trade-tariff-frontend,alphagov/trade-tariff-frontend,alphagov/trade-tariff-frontend,alphagov/trade-tariff-frontend,bitzesty/trade-tariff-frontend,alphagov/trade-tariff-frontend,bitzesty/trade-tariff-frontend