How do I find out which php file the logo code is in?

Website is thesloeruin.com

In the top left corner is a logo. I have inspected the element but unsure how to find out which php file its in and I have checked the obvious ones like header.php index.php etc.

The logo was added in using Appearance>Customise then selecting the dropdown menu Logo.

And the reason I want to find this line of code is so I can add an id or class to it and give it an animation.

Can someone please help me I have been stuck on this for a while.