At this point time I'm assuming jQuery uses exactly the same format as CSS does when using CSS selectors.
However, I have the following line in my JS (with a log to try and find the problem)
boxheight = $('.item .active > .html-carousel-slide > .slide-content-box').height();
You have the element
<div class="item active"> in your HTML and are trying to select it with
.item .active which is incorrect. Use
.item.active instead. The space between the classes says select all elements that have the class
active that are descendants of all elements with the class
item. What you really wanted to say was select the elements that have both the item and active classes, which you do by removing the space between the two.