// Tailored for extra small devices like portrait phones below 576px in width
@media (max-width: 575.98px) { ... }
// Designed for small devices such as landscape phones from 576px and above
@media (min-width: 576px) and (max-width: 767.98px) { ... }
// Optimized for medium-sized devices including tablets starting from 768px up to 991.98px
@media (min-width: 768px) and (max-width: 991.98px) { ... }
// Suitable for large devices like desktops ranging from 992px to 1199.98px
@media (min-width: 992px) and (max-width: 1199.98px) { ... }
// Ideal for extra-large devices like big desktop screens with a minimum width of 1200px
@media (min-width: 1200px) { ... }
Source of the code sample can be found at: https://getbootstrap.com/docs/4.1/layout/overview/
Why use .98px? Is it for ensuring cross-browser compatibility?
For more insights, check out: What are the rules for CSS media query overlap?