Combination of Automattic's _s theme and Bootstrap 4 by holger1411.
http://understrap.com
Frameworks · WordPress Theme
Get access to data on 15,227 websites that are UnderStrap Customers. We know of 8,268 live websites using UnderStrap and an additional 6,959 sites that used UnderStrap historically and 3,895 websites in the United States.
Get a list of 15,227 websites using UnderStrap which includes location information, hosting data, contact details, 8,268 currently live websites and an additional 7,164 domains that redirect to sites in this list. 6,959 sites that used this technology previously and 3,895 websites in the United States currently using UnderStrap.