Cannot get thumbnail to left align on Blog page

I didn’t set up the site below, but I am in charge of maintaining it. The thumb that is above the excerpt needs to be on the left side of the text. I have tried several things, but nothing seems to work.

I have tried adding to the CSS using the Custom CSS plugin so I am not editing the Twenty Thirteen theme itself.

Will the following code work and, if so, where does it need to go…what attribute does it need to be added to?

clear: both;
float: left;

https://moluccachocolate.com/blog/