Bootstrap

Bootstrap is an open-source front-end framework that concentrates on creating websites in a mobile-friendly environment. It enables quicker website building without much consideration of the basic commands and functions.
Web developers only have to insert the code into a pre-defined grid system. Also, this framework is built on HTML, CSS, and JavaScript.
Customisation, a feature of Bootstrap, helps users build their brands aesthetically by providing a set of default styling options.

It also ensures cross-browser compatibility, which adds to the consistency over all of the modern browsers.

Bootstrap is known for its strong community and well-maintained documentation. Many resources, tutorials, and third-party plugins help with learning and extending Bootstrap.