You can use ngStyle
to dynamically add the css
to your page from json.
<div [ngStyle]="{'color': variable ? 'red' : 'blue'}"></div>
An another example:
<div md-card-avatar [ngStyle]="{'background-image': 'url(' + post.avatar + ')', 'background-size': 'cover' }"></div>
here I have loaded background image from json-data.