/* disable element and their childs */

.disable {

  /* Note: pointer-events not supported by IE10 and under */

  pointer-events: none;

  opacity: 0.4;

}

​

/* Disable scrolling on child elements */

.disable div,

.disable textarea {

  overflow: hidden;

}

.disabledbutton {

    pointer-events: none;

    opacity: 0.4;

}

<input type="text" name="username" value="admin" >

​

<style type="text/css">

input[name=username] {

    pointer-events: none;

 }

</style>