Bootstrap 4 is designed to be responsive to mobile devices. Mobile-first styles are part of the core framework. The width=device-width part sets the width of the page to follow the screen-width of the device (which will vary depending on the device).

Variable defaults Every Sass variable in Bootstrap includes the !default flag allowing you to override the variable's default value in your own Sass without modifying Bootstrap's source code. Copy and paste variables as needed, modify their values, and remove the !default flag.

Another way of importing Bootstrap to HTML is to directly download the files locally to your HTML project folder. The files can be downloaded from the following links: Bootstrap 4: https://getbootstrap.com/docs/4.3/getting-started/download/ Bootstrap 5: https://v5.getbootstrap.com/docs/5.0/getting-started/download/

The form elements in Bootstrap 4 have defaulted to the browser-provided view. However, in Bootstrap 5, the form elements have a custom design that enables them to have a consistent look and feel in all browsers. The new form controls are based on completely semantic, standard form controls.