Describe the bug
Since the theme preview is a distinct URL, it gets added to browser history.

When I preview a theme, I see a button that says <- Back. When I click that it takes me back to the theme I was viewing. If i want to get back to the original grid, I need to find the breadcrumb to do so which isn't that easy to find. If I click my browser's back button, I will end up in the preview again. This isn't expected because I assume I reversed my navigational course when i clicked the "back" button in the preview.

To Reproduce
Steps to reproduce the behavior:

1. Go to wp.org/themes/
2. Choose a category
3. Click on any theme
4. Click preview
5. Click the "back" button in the preview window
6. Click your browser's back button
7. Notice you are back in the preview.

The only way to get back is to click "Theme Directory" and if you do, you lose your original filtering on the grid. So if you do preview, you lose all your progress unless you keep clicking back through the preview which doesn't feel like the right thing to do.

Expected behavior
I would expect that clicking back in my browser from the single page would take me back to the grid.

Video
https://d.pr/i/xoX6wd