Styling for tan background link lists

[joshdarby]

Changes

This pull request makes the following changes:

• Adds tan background styling option for the HTML link lists

Why

For #71 kinda

Testing/Questions

Features that this PR affects:

• HTML link lists

Steps to test this PR:

1. Paste this HTML in a text widget on a series landing page

   <div class="tan-background">
   <div class="tan-background-inner">
       <label class="special-projects-flex-container-title">3 Link Boxes</label>
           <div class="special-projects-flex-container">
               <div class="special-projects-container-inner-col">
                   <img class="alignnone wp-image-4960980 size-medium" src="https://citylimits.test/wp-content/uploads/2019/06/kingsbridge-heights-336x215.jpg" alt="" width="336" height="215" />
                   <h4>Label</h4>
                   <ul>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                   </ul>
               </div>
               <div class="special-projects-container-inner-col">
                   <img class="alignnone wp-image-4960980 size-medium" src="https://citylimits.test/wp-content/uploads/2019/06/kingsbridge-heights-336x215.jpg" alt="" width="336" height="215" />
                   <h4>Label</h4>
                   <ul>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                   </ul>
               </div>
               <div class="special-projects-container-inner-col">
                   <img class="alignnone wp-image-4960980 size-medium" src="https://citylimits.test/wp-content/uploads/2019/06/kingsbridge-heights-336x215.jpg" alt="" width="336" height="215" />
                   <h4>Label</h4>
                   <ul>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                       <li><a href="https://google.com">Link</a></li>
                   </ul>
               </div>
           </div>
       </div>
   </div>
   </div>

2. Make sure it looks ok on desktop and mobile

[benlk]

On the custom series landing page template's #sidebar-bottom, do we want to remove the Largo default 24px margin-bottom on .widget?

.widget {
    margin-bottom: 24px;
}