Yes you can add this to your .hentry css
box-shadow: -5px 6px 12px -4px #9B9191;
makes sure to use your child theme’s style.css file instead of changing the main theme’s css
If you think it’s not dark enough you can change the color at the end #9B9191 to “black”.
Don’t forget to pre-fix your Css to support most modern browsers:
-moz-box-shadow: 1px 1px 1px 1px #9B9191;
-webkit-box-shadow: 1px 1px 1px 1px #9B9191;
box-shadow: 1px 1px 1px 1px #9B9191;
You can also play around with this generator – choose box shadow, choose your values, and it will generate the CSS for you to copy and paste.
For more info on learning how to use drop shadow, check out CSS Tricks:
https://css-tricks.com/snippets/css/css-box-shadow/
Keep in mind that since this is Css3, it is not supported in IE8 or less. Hope that helps. 🙂