angular.js bootstrap ui - how do I change css styles?

I am using bootstrap UI with angular directives. And I want to change the default styles bootstrap applies for its elements. Should I target the HTML contents from the template? For example from here, I use accordion. When I define it in HTML, it has the following structure:

<accordion>
    <accordion-group heading="my heading">
      content here
    </accordion-group>

But when the directive processes the template it turns it into the following HTML:

<accordion close-others="oneAtATime"><div class="panel-group" ng-transclude="">
    <div class="panel panel-default ng-isolate-scope" heading="my heading">
        <div class="panel-heading">
            <h4 class="panel-title">
                <a class="accordion-toggle" ng-click="toggleOpen()" accordion-transclude="heading">
                    <span ng-class="{'text-muted': isDisabled}" class="ng-binding">content here</span>
                </a>
            </h4>
        </div>
        <div class="panel-collapse collapse" collapse="!isOpen" style="height: 0px;">
        <div class="panel-body" ng-transclude=""><span class="ng-scope">some content here</span></div>
    </div>

As you can see, it changes it quite significantly. So if I wanted to change how panel title is displayed, should I write in my css files

div.panel {}

and hope that the template doesn't change in the future?

What is the general approach to changing styles for HTML elements generated by directive's templates?