First change your link hover CSS to this:
.entry-content a:not(.button), .featured-image .wp-caption-text a {
box-shadow: inset 0 -1px 0 currentColor;
transition: color 100ms ease-in,box-shadow .13s ease-in-out;
}
.entry-content a:not(.button):focus, .entry-content a:not(.button):hover,
.featured-image .wp-caption-text a {
box-shadow: inset 0 0 0 currentColor,0 3px 0 currentColor;
}
And then add this CSS to align the caption left and give it a little space between the image.
.featured-image .wp-caption-text {
margin-top: 10px;
text-align: left;
}