Checkbox readonly

How do readonly checkbox by css.

HTML

<form id="aform" name="aform" method="POST">
    <input name="chkBox_1" type="checkbox" checked value="1" readonly />
    <br/>
    <input name="chkBox_2" type="checkbox" value="1" readonly />
    <br/>
    <input id="submitBttn" type="button" value="Submit">
</form>

CSS

input[type="checkbox"][readonly] {
  pointer-events: none;
}