HTML - CSS: Styling <object>?

You already add size and width to the object style="width: 100px; height: 100px;"

Example

You can assign an id or class for the object tat, that is perfectly correct. If you want the object to adapt to the width of its parent, just set its width to 100%. If you are using the <object> to embed flash, set the width for the <embed> tag also.

An object tag can be styled using CSS. Ref link text

The reason width didn't work in your example is that its a HTML attribute only and not accessible with CSS (see list in link above).

I would recommend that you put the object into a wrapper div (give the object a width of 100%) and control the width of the wrapper div with css.