This is Material Design Lite- Google Developers Blog

Material Design Lite (MDL) is introduced as a lightweight, responsive front-end framework that allows developers to implement Material Design principles in their web applications. MDL is built with CSS, JavaScript, and HTML, and is designed to be independent of specific JavaScript frameworks, making it versatile for various web development projects. It provides a set of pre-built components and styles that adhere to Material Design guidelines, enabling developers to create visually appealing and consistent user interfaces.