w3-css and div alignment


Is it possible to place a w3-css in an external file and not only inline?
What i want to do is align the <div> below 30px from the top. Is there a w3 margin?

<div class="w3-bar w3-card w3-blue-gray w3-margin-bottom w3-padding margin-top: 0px margin-top:30px"></div>

And is it necessary to have both "w3-bar and w3-card"? In my head they are the same with different value/purpose?

w3-***** is the css framework to w3 schools.
The inline styles (like style="position:...;") are bad and you should avoid them as long as it possible :)
Whay you are mixing classes with styles in the class attribute?
Css frameworks are usefull and many popular css frameworks are very complex but in real application/website faster or later you will have the situation when the css framework will be not enough and own css class will be needed.
Try to use as many as possible classes from the css framework, then try to use your own css classes and then when you can find needed class then you can create new one