Displaying multiple images in a row in Gallery

I’m migrating my photography website to Ghost, but am running into a snag trying to display multiple images in a row.

In my existing website, I can display the following:

As you can see, it renders 5 images in a row.

I tried to do the same in Ghost where I made a “Gallery” and added 5 images there, but it does not render all of them in a row and breaks them up into multiple rows.

Example: Imgur: The magic of the Internet

I am using the London theme for reference.

Is there a way to update it so that Gallery can display multiple images in a row (at least 5) without breaking into rows?

What CSS classes do I need to update via Code Injection to achieve this?