Depending on your preference there are several methods to add bootstrap styling to Angular 6 app.
Get bootstrap compiled assets:
Copy the links to the main app file or index.html of your angular project as shown below
<title>My Demo Angular App</title>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="icon" type="image/x-icon" href="favicon.ico">
Method 2: Install bootstrap, jquery and popper (required for bootstrap 4) using node packet manager (npm).
Run the following command
npm install bootstrap jquery popper.js
Optionally you can also install font-awesome to go with bootstrap theme.
npm install font-awesome
Once installed, all these dependencies are available in node_modules folder of your application directory.
Next open angular.json file located in your application root. (previously it was angular-cli.json)
Find the “styles” and “scripts” tags and place the following code:
Save and you are ready to use bootstrap on your angular project!