Okay, I have two more suggestions, as shown in the picture. The parts underlined in red are where I think improvements should be made:
-
The header is too wide and takes up too much space; I suggest reducing its height slightly.
-
Compared to the right side, the left side has a larger width and denser content, while the right side has a smaller width. Once there is a colored background, the balance is clearly lost. It becomes more uncomfortable on larger display screens.
I suggest using a light gray for the background color, increasing the width of the right sidebar, and adding some expandable function buttons. I found a reference case with a similar style:
Reference: https://mail.google.com/chat