Radio

<div class="form-group">
  <div class="mb-2 flex items-center">
    <input class="form-input-radio" type="radio" name="radio_default" id="radio_default_1">
    <label class="ml-2" for="radio_default_1">
      Default radio
    </label>
  </div>
  <div class="flex items-center">
    <input class="form-input-radio" type="radio" name="radio_default" id="radio_default_2" checked>
    <label class="ml-2" for="radio_default_2">
      Default checked radio
    </label>
  </div>
</div>

<!-- ActionView::Helpers::FormTagHelper -->
<div class="form-group">
  <div class="mb-2 flex items-center">
    <%= radio_button_tag "radio_default", "1", false, class: "form-input-radio" %>
    <%= label_tag "radio_default_1", "Default radio", class: "ml-2" %>
  </div>

  <div class="flex items-center">
    <%= radio_button_tag "radio_default", "2", true, class: "form-input-radio" %>
    <%= label_tag "radio_default_2", "Default checked radio", class: "ml-2" %>
  </div>
</div>

<!-- ActionView::Helpers::FormHelper -->
<%= form_with model: @form do |f| %>
  <div class="form-group">
    <div class="mb-2 flex items-center">
      <%= f.radio_button_tag "radio_default", "1", false, class: "form-input-radio" %>
      <%= f.label :radio_default_1, "Default radio", class: "ml-2" %>
    </div>

    <div class="flex items-center">
      <%= f.radio_button_tag "radio_default", "2", true, class: "form-input-radio" %>
      <%= f.label :radio_default_2, "Default checked radio", class: "ml-2" %>
    </div>
  </div>

  <%= f.submit class: "btn btn-primary" %>
<% end %>

/ ActionView::Helpers::FormHelper
= form_with model: @form do |f|
  .form-group
    .mb-2.flex.items-center
      = f.radio_button_tag "radio_default", "1", false, class: "form-input-radio"
      = f.label :radio_default_1, "Default radio", class: "ml-2"
    .flex.items-center
      = f.radio_button_tag "radio_default", "2", true, class: "form-input-radio"
      = f.label :radio_default_2, "Default checked radio", class: "ml-2"
  = f.submit class: "btn btn-primary"