I would re-try adding css using the media definition but this time, put a !important
to your css attribute.
.widget input {
width: 200px !important;
}
From http://en.wikibooks.org/wiki/Cascading_Style_Sheets/Important
The important keyword makes a declaration take precedence over normal declarations—those that are not tagged with the important keyword. So "p { color: red ! important }" takes precedence over "p { color: green }".