Fix branches panel at smaller screen sizes

app/assets/stylesheets/bootstrap_migration.scss

@@ -131,6 +131,10 @@ table {
 }
 
 .card {
+  .card-title {
+    margin-bottom: 0;
+  }
+
   &.card-without-border {
     @extend .border-0;
   }

app/views/projects/branches/_branch.html.haml

@@ -28,7 +28,7 @@
         = s_('Branches|Cant find HEAD commit for this branch')
 
   - if branch.name != @repository.root_ref
-    .divergence-graph.d-none.d-sm-block{ title: s_('%{number_commits_behind} commits behind %{default_branch}, %{number_commits_ahead} commits ahead') % { number_commits_behind: diverging_count_label(number_commits_behind),
+    .divergence-graph.d-none.d-md-block{ title: s_('%{number_commits_behind} commits behind %{default_branch}, %{number_commits_ahead} commits ahead') % { number_commits_behind: diverging_count_label(number_commits_behind),
       default_branch: @repository.root_ref,
       number_commits_ahead: diverging_count_label(number_commits_ahead) } }
       .graph-side
@@ -39,7 +39,7 @@
         .bar.bar-ahead{ style: "width: #{number_commits_ahead * bar_graph_width_factor}%" }
         %span.count.count-ahead= diverging_count_label(number_commits_ahead)
 
-  .controls.d-none.d-sm-block<
+  .controls.d-none.d-md-block<
     - if merge_project && create_mr_button?(@repository.root_ref, branch.name)
       = link_to create_mr_path(@repository.root_ref, branch.name), class: 'btn btn-default' do
         = _('Merge request')