For the main page, the subheader has a background image

<div class="mm-subheader ">
...
</div>

The image can be changed from app/css/scss/_site-header.scss

For the other pages, the subheader has the following code:

<div class="mm-subheader--bg mm-subheader--light flex">
 <div class="mm-subheader__container">
  <div class="container custom_width">
  <!--breadcrumb section -->
   <ul class="mm-breadcrumb breadcrumb">
     <li><a href="#">Home</a></li>
     <li>Cart</li>
   </ul>
   <!--title section -->
   <div class="subheader-title">
    <h2 class="subheader-title__main-title">Cart</h2>
   </div>
  </div>
 </div>
</div><!--end subheader-->