Notion has two appearances — light & dark.
Try using Notion’s built-in emojis/icons first.
The latest icons will automatically adjust themselves according to the mode you use! Check out the icon of this callout :D
If you’re using custom icons, make sure they’re visible in both modes.
The common mistake is using a white icon on a dark Notion. You can’t see it in light mode!
If you’re adding illustrations, ensure they’re visible in dark mode too.
The background may have been removed improperly in the PNG format, but you see no issue in light mode!
If your template looks better in dark mode, mention it :D