Input with display:block is not a block, why not?

Check out what I came up with, a solution using the relatively unknown box-sizing:border-box style from CSS 3. This allows a 'true' 100% width on any element regardless of that elements' padding and/or borders.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html;charset=utf-8">

        <title>Cross-browser CSS box-sizing:border-box</title>

        <style type="text/css">
            form {display:block; margin:0; padding:0; width:50%; border:1px solid green; overflow:visible}
            div, input {display:block; border:1px solid red; padding:5px; width:100%; font:normal 12px Arial}

            /* The voodoo starts here */
            .bb {
                box-sizing: border-box; /* CSS 3 rec */
                -moz-box-sizing: border-box; /* Firefox 2 */
                -ms-box-sizing: border-box; /* Internet Explorer 8 */
                -webkit-box-sizing: border-box; /* Safari 3 */
                -khtml-box-sizing: border-box; /* Konqueror */
            }
        </style>

        <!-- The voodoo gets scary. Force Internet Explorer 6 and Internet Explorer 7 to support Internet Explorer 5's box model -->
        <!--[if lt IE 8]><style>.bb {behavior:url("boxsizing.htc");}</style><![endif]-->
    </head>

    <body>
        <form name="foo" action="#">
            <div class="bb">div</div>
            <input class="bb" size="20" name="bar" value="field">
        </form>
    </body>
</html>

This solution supports Internet Explorer 6 and Internet Explorer 7 via a behaviour written by Erik Arvidsson with some tweaks from Dean Edwards to support percentage and other non-pixel widths.

Working example
Behaviour (boxsizing.htc)


The reason this happens is that a text input's size is determined by its size attribute. add size="50" inside the <input> tag. Then change it to size="100" -- see what I mean?

I suspect there's a better solution, but the only one that comes to mind is something I found on the "Hidden features of HTML" question on SO: Use a content-editable div, instead of an input. Passing the user input to the enclosing form (if that's what you need to) might be a little tricky.

Hidden features of HTML


Your best bet is to wrap the input in a div with your border, margins, etc., and have the input inside with width 100% and no border, no margins, etc.

For example,

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
    <head>
        <title>width:auto</title>

        <style>
            div {
                border: 1px solid red;
                padding: 5px;
            }
            input, form {
                display: block;
                width: 100%;
            }
        </style>
    </head>

    <body>
        <form>
            <div><input type="text" name="foo" /></div>
        </form>
    </body>
</html>

Tags:

Html

Css

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