<%= simple_form_for(@listing) do |f| %>
    <%= f.error_notification %>
    <div class="form-inputs">
      <%= f.input :title %>
      <%= f.input :description %>
      <%= f.input :fair_market_value, input_html: { type: "number", step: "0.01", value: "0.00" } %>
      <%= f.label :category %>
      <%= f.collection_select :category_ids, Category.order(:name), :id, :name, {}, { multiple: false } %>
    </div>

    <div class="form-actions">
      <%= f.button :submit %>
    </div>
<% end %>

<%= simple_form_for(@listing) do |f| %>
    <%= f.error_notification %>
    <div class="form-inputs">
      <%= f.input :title %>
      <%= f.input :description %>
      <%= f.input :fair_market_value, input_html: { type: "number", step: "0.01", value: "0.00" } %>
      <%= f.label :category %>
      <%= f.collection_select :category_ids, Category.order(:name), :id, :name, {}, { multiple: false } %>
    </div>

    <div class="form-actions">
      <%= f.button :submit, class: "radius" %>
    </div>
<% end %>

Add radius to new item form button
Add radius to new item form button
