Big-Sur friendly theme I made for VScode extension https://marketplace.visualstudio.com/items?itemName=eyhn.vscode-vibrancy

Dark (Only Subbar).css

.monaco-workbench,
.monaco-workbench .sidebar,
.monaco-workbench .part.panel.right,
.monaco-workbench .part.panel .pane-body.integrated-terminal .terminal-outer-container,
.composite.title,
.pane-header.expanded,
.activity-bar-placeholder,
.monaco-workbench .activitybar,
.monaco-workbench .monaco-list-rows,
.monaco-editor .margin,
body {
	background: transparent !important;
}

.monaco-list-row.selected {
	border-radius: 25px;
}

.monaco-workbench.fullscreen {
	background-color: #202020 !important;
}

pretty cool huh?

Go into vibrancy extensions's folder (for Mac OS it's in ~/.vscode/extensions/), go into a folder with the name 'vibrancy' in it. Replace themes/Dark (Only Subbar).css with this code. Go back into Vscode, switch to light mode theme, then back to 'Dark (Only Subbar)' then reload the app.

Using Github Dark colour scheme

The title bar is removed with CustomizeUI and put this code into settings.json

{
    ...
    "window.titleBarStyle": "native",
    "customizeUI.titleBar": "inline",
    ...
}