how to make a div focusable code example

Example 1: how to make a div scrollable

<div id="" style="overflow:scroll; height:400px;">

Example 2: css disable input

<input type="text" name="username" value="admin" >
<style type="text/css">
  input[name=username] {
    disabled: true; /* Does not work */
  }
</style>

Example 3: html how to make element focusable

tabindex="0"