There are two unique instances where featured images are shown in this theme. The first is a bit more simple since the theme loads the square formatted images. These can be properly "circled" with the following added to the style.css
:
.type-post.has-post-thumbnail > a {
line-height: 0;
overflow: hidden;
border-radius: 50%;
}
Available classes for the above
HOMEPAGE RECENT POSTS
simple-grid one-third first post-2308 post type-post status-publish format-standard has-post-thumbnail category-health-wellness entry
SIDEBAR MOST VIEWED
post-2070 post type-post status-publish format-standard has-post-thumbnail category-get-motivated category-inspiration category-something-to-do entry
These ones are a bit more tough since the theme doesn't load the square image, but the original. This means the image will need to be manipulated to always be 100% the height of the container it lies within but unfortunately that assumes all images are landscape square, and not portrait.
Here's a rough attempt in pure CSS
img.post-image.entry-image {
float: none;
width:100%;
height:100%;
}
header.entry-header > a {
width: 215px; /* you wont want to hard code the height here, since widths will change based on browser window width */
height: 215px;
overflow: hidden;
border-radius: 50%;
display: block;
}
Available classes
simple-grid one-third odd first post-2070 post type-post status-publish format-standard has-post-thumbnail category-get-motivated category-inspiration category-something-to-do entry