How to align the radio buttons horizontally in angular material?

You do not need to override any default CSS:

<md-radio-group layout="row">
  <md-radio-button value=0 class="md-primary">On</md-radio-button>
  <md-radio-button value=1> Off </md-radio-button>
</md-radio-group>

Just put in md-radio-group tag a layout="row" attribute.

Better not override any existing class.

Use the directive ng-style and give value for display parameter.

<md-radio-group ng-model="selvalue">
  <md-radio-button value="A" class="md-primary" ng-style="{'display':'inline'}"> Apple</md-radio-button>
  <md-radio-button value="R" class="md-primary" ng-style="{'display':'inline'}"> Orange </md-radio-button>
</md-radio-group>