Ion-nav-bar some of the ion tags not working

I’m using Android Studio for Ionic projects… I’m new to Ionic, in my project none of the ion tags are working, CSS styles and classes are working…
, and so on are not working…
Can any one suggest me… where i did mistake…
Below is my code… In this code

<ion-view view-title="gayatri"></ion-view> this part wasn’t working


<link href="lib/ionic/css/ionic.css" rel="stylesheet">
<link href="css/style.css" rel="stylesheet">

<!-- IF using Sass (run gulp sass first), then uncomment below and remove the CSS includes above
<link href="css/" rel="stylesheet">

<!-- ionic/angularjs js -->
<script src="lib/ionic/js/ionic.bundle.js"></script>

<!-- cordova script (this will be a 404 during development) -->
<script src="cordova.js"></script>

<!-- your app's js -->
<script src="js/app.js"></script>