Hide or Resize featured image on blogpost?? (Image too huge!)

Site URL: https://weearnmedia.com

Hi! I feel like this should be easy and I've seen similar queries on the forum, but everything I'm trying isn't working. 

Simple, I would like to add some code to hide the featured thumbnail image on every single blogpost page on the site. When you visit-- you see a HUGE image of our podcast guests's face, and it's just not aesthetically pleasing at all. Would love to ideally hide it forever while maintaining the ability to have a thumbnail image (so that it populates our homepage). 

Any ideas? 

Example blogpost: https://www.weearnmedia.com/episodes/michelle-rafter (help me get rid of these GIANT images!) 

Add to Home > design > Custom CSS

section.blog-item-banner.has-main-image {
    display: none;
}