Thanks for the detailed description, that helps a lot.
If the preview shows the correct transparency but the front end keeps displaying a solid background, in most cases this is related to caching or CSS optimization rather than the setting itself not being saved. Very often the site continues loading an older generated stylesheet from cache, especially when server-side cache, CDN, or CSS minification is enabled.
Please try clearing all layers of cache, including any caching plugin, your hosting cache (Hostinger has its own cache layer), and CDN if you are using one. It’s also worth briefly testing in a private/incognito browser window or a different browser to rule out local browser caching. If you are using CSS/JS optimization or minification, try temporarily disabling it and check whether the transparency applies correctly.
If the issue still persists after that, please open a ticket in our support system and include the page URL, gallery ID, the lightbox mode you’re using, and information about active caching/optimization tools. We’ll take a closer look and reproduce the situation on our side
