bootstrap screen sizes

1// Extra small devices (portrait phones, less than 576px)
2@media (max-width: 575.98px) { ... }
3
4// Small devices (landscape phones, 576px and up)
5@media (min-width: 576px) and (max-width: 767.98px) { ... }
6
7// Medium devices (tablets, 768px and up)
8@media (min-width: 768px) and (max-width: 991.98px) { ... }
9
10// Large devices (desktops, 992px and up)
11@media (min-width: 992px) and (max-width: 1199.98px) { ... }
12
13// Extra large devices (large desktops, 1200px and up)
14@media (min-width: 1200px) { ... }

1// Small devices (landscape phones, 576px and up)
2@media (min-width: 576px) { ... }
3
4// Medium devices (tablets, 768px and up)
5@media (min-width: 768px) { ... }
6
7// Large devices (desktops, 992px and up)
8@media (min-width: 992px) { ... }
9
10// Extra large devices (large desktops, 1200px and up)
11@media (min-width: 1200px) { ... }

1The Bootstrap grid system has four classes:
2xs (for phones - screens less than 768px wide)
3sm (for tablets - screens equal to or greater than 768px wide)
4md (for small laptops - screens equal to or greater than 992px wide)
5lg (for laptops and desktops - screens equal to or greater than 1200px wide)

1<div class="container">
2  <div class="row">
3    <div class="col">
4      1 of 3
5    </div>
6    <div class="col-6">
7      2 of 3 (wider)
8    </div>
9    <div class="col">
10      3 of 3
11    </div>
12  </div>
13  <div class="row">
14    <div class="col">
15      1 of 3
16    </div>
17    <div class="col-5">
18      2 of 3 (wider)
19    </div>
20    <div class="col">
21      3 of 3
22    </div>
23  </div>
24</div>