Bootstrap actually doesn’t use classes like pad-10 or mar-left-10 directly.
Instead, it provides a set of very flexible utility classes for spacing, like p-1 through p-5 for padding and m-1 through m-5 for margins.
For example, pl-3 adds left padding, and ml-4 adds left margin.
These classes are based on a spacing scale, so you don’t get to specify exact pixel values but predefined increments. It’s super convenient once you get used to it!