Thank you so much for your kind response. I am already using the Review Heatmap add-on. I thought that the two add-ons might be conflicting, so I tried disabling it, but the result was the same. The one I want to use is indeed Enhance Main Window.
When I install Enhance Main Window, this is what it looks like. It seems like I can reduce the width by removing some items, but why do the profile picture and font change? I installed Enhance Main Window from here.