Bttn.css is a collection of most stylish css button with animated visual feedback. You can adjust the colors, sizes and width of the buttons and pretty easily. Just include the library and add necessary classes to get the desired style.
CSSPin is a collection of beautiful and creative pure css spinners or loaders. It can easily be added with npm script or just or including the library in a webpage. It's highly customizable and deserves a checkout.
CSS Checkbox Library is just another awesome collection of custom css checkboxes. You can find many variations to use in your project. It's easy and simple to integrate.
CSSGram is very tiny css library to recreate image filters like instagram. The filters are purely created in css using various gradients and blending techniques. Just few simple classes to integrate.
Hint.css is a pure css based lightweight tooltip library. You just to need to include the stylesheet and plugin the necessary classes in your elements and done. Now as you hover over the elements the tooltip will be visible at the location you chose. The library requires a license for use with commercial websites.
Pretty Checkbox is another pure css library to beautify checkboxes and radio boxes. The website has pretty extensive list of customization options to get your desired checkbox controls. The library also comes in scss format which allows you to enable or disable other unused styling options very easily.
Social Share Kit is a helper library for social share buttons, icon sets, floating or sticking button group. The homepage lists the various buttons and styles you can make use of with the library. It has a responsive layout which makes it better fit for use with mobile devices and has various meaningful customization options. The library requires a license for commercial use though.
The Box Shadows CSS is a collection of well crafted box shadow styles which you can use in with your css to enhance shadow effects. The website also offers an added ability to customize your box shadows in a easy way.
Three Dots as the name suggests is a collection of beautifully animated css spinnners using only dots. The collection is really creative and inspiring. You can integrate it easily in your project, you just to need to include the library and plug the required classes.
Epic Spinners is another collection of well crafted and beautifully animated css spinners also offers a vue js integration though. You can just click on a spinner to copy the html structure and the associated styles to use it. It's very stylish, creative and modern.
Basic Scroll is a library to that gives you ability to changes css variables depending on the scroll position. The variables can directly be used within the css to animate items. The library also has a good support for mobile devices as well. You can find more information on the library homepage.
There are well many libraries available on the web, one better than the other. This was just a simple collection of few of those.