How to disable button's default onclick background effect in template node?

Hi there,

can anyone help me removing the gray background when i click on button?
Template node code, what i tried so far:

<style>

.container
{
    overflow: hidden !important;
}

.btn,
.btn:focus,
.btn:active
{
    margin: 0 !important;
    padding: 0 !important;
    background: none !important;
    outline: none !important;
    box-shadow: none !important;
}
</style>

<div class="container">
    <md-button ng-if="msg.payload === '0'" class="btn" ng-click="send({payload: 'switch_on'});">
        <img  src="/myimages/bulb_dark.png" alt="bulb_dark.png" width="45" height="45">
    </md-button>
    <md-button ng-if="msg.payload === '1'" class="btn" ng-click="send({payload: 'switch_off'});">
        <img  src="/myimages/bulb_light.png" alt="bulb_light.png" width="45" height="45">
    </md-button>
    <span>Schreibtisch</span>
</div>

"onclick" effect looks like:
onlick_effect

Thanks in advance and greetings from germany!