what do css classes like my-2, my-lg-0, mr-sm-2 do in bootstrap 4? [duplicate]

Answer 1

Those are bootstrap spacing utilities classes :

mr-sm-2:

r - for classes that set margin-right or padding-right

my-2, my-lg-0:

y - for classes that set both *-top and *-bottom

the m

m - for classes that set margin

you can see the notation from boostrap spacing here

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sm and lg are utilities classes that everyone who uses bootstrap are use to see it:

sm - small

lg - large