ExtSearch/src/build/sources/less/themes/flow_xs.less

body {
    .d3_extsearch_navigation {
        &.d3theme_@{d3_class_themeid} {
            &.d3sidebar {
                #d3searchfilterform .item {
                    .make-xs-column(@grid-columns);
                }
            }
        }
    }
}