How to style Theme using Bootstrap

I imported Bootstrap into my Theme. There are a lot of components in lms-main and bootstrap having the same class name such as “btn” or “row”,… So what I’ve done is overriding all of them, something like:

.btn {
  background-color: red;
}

Obviously It’s worked, buttons turned into red color. But in xBlock, the style is from lms-course so there isn’t the override-thing.

What is the accurate way to custom the theme using Bootstrap