Small businesses build their websites by setting up on a platform like Shopify or Squarespace. They use a template and fill in the content. They add functionali

Small businesses build their websites by setting up on a platform like Shopify or Squarespace. They use a template and fill in the content. They add functionality to the site, like an email opt-in, a "free shipping if you order over $50" bar at the top of the page, a "contact us" button floating at the bottom, a bunch of social media icons floating on the side... via plug-ins/apps/scripts. They don't ever touch code. All those plug-ins/apps/scripts that provide this functionality to non-technical website owners as a service have no idea what the webpage DOM will look like, how it's coded, what other scripts you're loading on the page. They end up fighting to be on top with z-indexes, and that's how you end up with the website's main navigation being on top of instead of behind a modal dialog like a popup contact form, when the site owner wants it to be behind. This "top layer" means the stuff that isn't part of the page and should always be above the page can really be on top.