app/views/catalog/_per_page_widget.html.erb
<%# Override from blacklight to change the button class to btn-outline-primary %>
<% if show_sort_and_per_page? %>
<span class="sr-only visually-hidden"><%= t('blacklight.search.per_page.title') %></span>
<%= render(Blacklight::System::DropdownComponent.new(
param: :per_page,
choices: per_page_options_for_select,
id: 'per_page-dropdown',
search_state:,
selected: current_per_page,
interpolation: :count
)) do |w| %>
<%= w.with_button classes: 'btn btn-outline-primary dropdown-toggle', label: w.button_label %>
<% end %>
<% end %>