Open your settings.json
in VS code (CMD P, search for settings), and update the shell for linux.
"terminal.integrated.shell.linux": "/usr/bin/zsh"
Then re-open the workspace.
Install FireMono font. Note that these should be installed locally if you're using VSCode's desktop app to use the CodeSpace
mkdir ~/.fonts
wget https://github.com/ryanoasis/nerd-fonts/releases/download/v2.0/FiraMono.zip
unzip -o -d ~/.fonts FiraMono.zip
rm FiraMono.zip
fc-cache -fv