On my UI, I have several buttons. I want to highlight those user have tapped for few seconds. Is there any directive or style I can use? Or I have to write my own?
Yes, what you are asking for is already available in angular-material. Just make sure you are making your buttons as below:
<md-button class="md-raised md-primary">Zero</md-button>
md-button is the directive and the class you specify will change the look and feel... say
md-select is there in angular-material. You can always group together buttons if you want, place them in an
md-list and they will behave as you want. And, yes,
md-dropdown are coming in next few releases.