If you have enabled animation and want to change size, you can change it in
ow_plugins\isearch\components\console_search.php
$jsCode .= '$("#isearch-box").focus(function(){
$(this).animate({ width: 350 }, "slow");
}).blur(function() {
var w = $(this).attr("data-default");
$(this).animate({ width: 150 }, "slow");
});';