3
You don’t do this through theme, but by applying your custom settings.
As described in documentation
As an example, this setting will change the color of folder names.
"workbench.colorCustomizations": {
"sideBar.foreground": "#fff"
}
Particularly I find it strange, but you can for example use "window.zoomLevel": -0.5
will zoom in on the whole vscode
(including the sidebar) and then to compensate you can set "editor.fontSize"
for your taste.