Microsoft will probably / hopefully fix this by making Loop's sidebar with an adjustable divider. Until then, this can help you when you have deep "folder" structures and pages with descriptive names that are lost in the sidebar's 320px limitations.

Fully packed extension on Google Chrome Web Store: https://chromewebstore.google.com/detail/custom-microsoft-loop-sid/nimkabpmmjnlbfhdhieenenpdecbhfip?hl=en