Content switching CSS for responsive emails - https://www.shopify.com/partners/blog/dirty-css-hacks-for-responsive-emails

dirty-css-hacks-for-responsive-email-content-switching.css

@media only screen and (max-width: 500px) { 
  table, tr, td {
    display: block; /* table-cell -> block */
    width: 100%; 
  }	
  
  .main-col { 
    display: table-header-group; 
  }
  
  .sub-col { 
    display: table-footer-group; 
  }					
}