How to make an element width: 100% minus padding?

Question

I have an html input.

The input has padding: 5px 10px; I want it to be 100% of the parent div\'s width(which is fluid).

However using widt

Answer 1

What about wrapping it in a container. Container shoud have style like:

{
    width:100%;
    border: 10px solid transparent;
}