BootStrap is a library of code that lets you quickly code your own mobile-friendly websites. It includes HTML, CSS and a JS library which lets you quickly build your own pages using the default BootStrap styling and interactions. You can create your own code to customise how your website looks and behaves (which we did for this website).
BootStrap is used throughout the web and is used by major companies and websites to build their webpages.
There is inbuilt support for mobile devices, and interactive elements such as dialog boxes, tooltips, progress bars, navigation dropdowns, and carousels. Each Bootstrap component consists of HTML which sets the components structure, CSS which sets how the component will look, and in some cases JavaScript code which adds interactivity.
You can learn more about BootStrap at the following sites: