You will have the stylesheets order like this, first you will include bootstrap css, then your stylesheet file. Why is that? Because that way you can overwrite the classes from the framework without using !important. You can write your own classes and include them in your layout, you can use bootstrap classes and make adjustments to them as you need. When you mix your classes and bootstrap classes check what attributes are added from their classes, do you need them or not etc...
Example
