Creating rounded corners on a container

Hello

I'm using GP Premium and I've looked in the docs and past forum responses, but couldn't find a solution.

Site: lyfebug.com

Trying to create rounded corners on a container "Swift 4.2 card" I created on the front page. This card isn't autogenerated, it was created manually so I can have a little more control over it. I gave the container the class name: my-rounded-corners and I added some css in simple css. It just doesn't seem to have any affect though.

Here is my css:
.my-rounded-corners {
border-radius: 50px;
}

Any help would be appreciated. Also wondering if there is a plugin that could tell me the way to access different parts of css for my site. I run into this a lot and I don't fully understand what I'm doing, but I know enough to be dangerous.

Thank you!