1. Install HTML CSS Support Extension in vscode. i.e: ext install vscode-html-css
2. Add an resource.json file inside your .vscode or project root folder, you can configure paths to your used style sheets.
3.Add the following code to the resource.json file
{
"css": {
"style": [
"replace_with_path_to_your_css_bootstrap_file" //i.e bower_components/bootstrap/dist/bootstrap.css
]
}
}