Basically, what this script does is to check if there is any ID named "image-gallery" and get the different list items that may exist within it. These elements will be displayed as thumbnails and a function will decide what to do once they are clicked. So, each time we click on a thumbnail, the "active" class will be assigned and the thumbnail should be visible in the larger container.
Step 7. Finally, save the changes by clicking the "Save template" button.
And here's the HTML code providing a normal list with the image-gallery ID, enclosed within a DIV with a relative position in order to avoid side effects of other pre-existing positions.
Step 8. Paste the below HTML to where you want to display the gallery by going either to "Layout" and adding a new gadget (click on the "Add a gadget" link and choose "HTML/JavaScript" option), or inside a post/page in the HTML section.