The icon in the sidebar/window bar looks out of place (too dark)

[krassowski]

In the current version the extension the icon is black:

Previously it was nicely integrated with the other icons:

[krassowski]

I think this was introduced during migration from JupyterLab 3 to 4 in #169. I am going to assume that this change was unintentional and open a tiny PR to change it back to what I believe is a nicer colour, I hope this is ok :)