Great idea! And thank you for the feedback. The background open feature will be in the next release: doing an alt + click on a folder or bookmark will open in a new tab and not switch to it.

As of version 3.0.2, there is support for custom CSS by opening the settings and selecting the curly brace icon in the upper right.

If you want to make the back button wider try this css:

.breadcrumb-container > button:first-of-type {
width: 60px;
display: flex;
justify-content: center;
}

Hope that addresses the issues you were having. If you have more suggestions, I would encourage you to open a discussion on the github page.