Add padding to HTML text input field

You can provide padding to an input like this:

HTML:

<input type=text id=firstname />

CSS:

input {
    width: 250px;
    padding: 5px;
}

however I would also add:

input {
    width: 250px;
    padding: 5px;
    -webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
    -moz-box-sizing: border-box;    /* Firefox, other Gecko */
    box-sizing: border-box;         /* Opera/IE 8+ */
}

Box sizing makes the input width stay at 250px rather than increase to 260px due to the padding.

For reference.