How to use the same name classes but in separate styles

see the example to understand:

    <!--Standard Bootstrap -->
    <link href="/build/css/site/bootstrap.min.css" rel="stylesheet">

    <!-- Material Design Bootstrap -->
    <link href="/build/css/site/mdb.min.css" rel="stylesheet">

so i want a thing like it:

    <div class="btn btn-danger" >Standard Bootstrap Button</div>
    <div class="btn btn-danger" >Material Design Bootstrap Button</div>

The name of the classes are the same. But they are in two separate styles. How can I use the two styles as I said?

Forgive me for the bad English.