Bootstrap is modular and consists essentially of a series of Less stylesheets that implement the various components of the toolkit. A stylesheet called "Bootstrap less" includes the components stylesheets. Developers can adapt the Bootstrap file itself, selecting the components they wish to use in their projects.
Adjustments are possible to a limited extent through a central configuration stylesheet. More profound changes are possible by the Less declarations.
The use of the Less stylesheet language allows the use of variables, functions and operators, nested selectors, as well as so-called mixins.