iOS 11 Glyphs is a new free and open source icon library from the fine folks at Icons8. Apple has changed the way tab icons are styled and presented in iOS 11. This resource will help you to use icons that fit these new specifications, or help inspire to design new icons of your own. Download includes icon assets in SVG, PDF and PNG formats.
Apple introduced a new icon style for the tab bar icons. They are not thin outline icons anymore; these are the solid icons. Apple calls them the glyphs.