We can see that now, the <header> element only have the kcFormHeaderClass, the login-pf-header class has been removed. As a result the text is now aligned to the left (default layout)
On some components, multiples utility classes are applied, you may want to keep some of them and remove others. Example:
Here we can see that a bunch of col-* classes gets applied to the element with kcInputWrapperClass
Let's say, for example, that we would like to remove keep only the col-md and lg classes. To do that that we would write: