HTML

no-gutter bootstrap 4

<div class="row no-gutters">
  <div class="col-12 col-sm-6 col-md-8">.col-12 .col-sm-6 .col-md-8</div>
  <div class="col-6 col-md-4">.col-6 .col-md-4</div>
</div>

no gutter in bootstrap css for row

.row.no-gutter {
  margin-left: 0;
  margin-right: 0;
}

.row.no-gutter [class*='col-']:not(:first-child),
.row.no-gutter [class*='col-']:not(:last-child) {
  padding-right: 0;
  padding-left: 0;
}