xs (phones), sm (tablets), md (desktops), and lg (larger desktops).
Each tier of classes scales up, meaning if you plan on setting the same widths for xs and sm, you only need to specify xs.
WHEN GOOD ENUF IS GREAT
Entire markets have been transformed by products that trade power or fidelity for low price, flexibility, and convenience.
— Erin Biba
S. Novaes. (2000)cite arxiv:hep-ph/0001283Comment: 101 pages, 14 figures, To be published in "Particle and Fields", Proceedings of the X J. A. Swieca Summer School (World Scientific, Singapore, 2000).