You can take the hint that this plugin will add class active
to current active image. So you can do like this to get your desired width:
var imgWidth = $(".cycle-slideshow").find("img.active").width();
then you can use this width value to set width for other element:
$("other element selector").width(imgWidth);
Edit
I assume HTML for your next
and prev
button look like this:
<div class="center">
<a href="#" id="prev">Prev</a>
<a href="#" id="next">Next</a>
</div>
Then you just need to do:
$("#prev, #next").on('click', function() {
var imgWidth = $('.cycle-slideshow').find(".cycle-slide-active").width();
$(".topbar").width(imgWidth);
});