Options apply standard CSS classes to the snippet. Depending on the method that you choose, the UI will behave differently.

data-select_class=" class name "

More data-select_class in the same group defines a list of classes that the user can choose to apply. Only one option can be enabled at a time.

data-toggle_class=" class name "

The data-toggle_class is used to apply one or more CSS classes from the list to a snippet. Multiple selections can be applied at once.
Let's demonstrate how default options work with a basic example.
We start by adding a new file in our views folder - name it options.xml and add the default Odoo XML markup. Create a new template copy/pasting the following

<template id="snippet_testimonial_opt" name="Snippet Testimonial Options" inherit_id="website_less.snippet_options">
  <xpath expr="//div[@data-js='background']" position="after">
    <div data-selector=".snippet_testimonial"> <!-- Options group -->
      <li class="dropdown-submenu">
        <a href="#">Your Option</a>
        <ul class="dropdown-menu"> <!-- Options list -->
          <li data-select_class="opt_shadow"><a>Shadow Images</a></li>
          <li data-select_class="opt_grey_bg"><a>Grey Bg</a></li>
          <li data-select_class=""><a>None</a></li>
        </ul>
      </li>
    </div>
  </xpath>
 </template>