Bootstrap 4
Bootstrap 4 Get Started
Bootstrap CDN, provided for free by the folks at MaxCDN. Using a package manager or need to download the source files? Head to the downloads page.

Bootstrap CDN :

Skip the download with the Bootstrap CDN to deliver cached version of Bootstrap’s compiled CSS and JS to your project.

<link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css" />

<script type="text/javascript" src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js"></script>

If you’re using our compiled JavaScript, don’t forget to include CDN versions of jQuery and Popper.js before it.

<script type="text/javascript" src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js"></script>
CSS :
Copy-paste the stylesheet <link> into your <head> before all other stylesheets to load our CSS.
JS :
Many of our components require the use of JavaScript to function. Specifically, they require jQuery, Popper.js, and our own JavaScript plugins. Place the following <script>s near the end of your pages, right before the closing </body> tag, to enable them. jQuery must come first, then Popper.js, and then our JavaScript plugins.
Responsive meta tag :
Bootstrap is developed mobile first, a strategy in which we optimize code for mobile devices first and then scale up components as necessary using CSS media queries. To ensure proper rendering and touch zooming for all devices, add the responsive viewport meta tag to your <head>.
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
HTML5 doctype :
Bootstrap requires the use of the HTML5 doctype.
<!doctype html>
<html lang="en">
  ...
  ...
  ...
</html>