CSS Containment (https://drafts.csswg.org/css-contain) is a new standard focused on improving the rendering performance of web pages by allowing the isolation of a subtree from the rest of the page. User agents that implement the “contain” property take advantage of this feature to apply strong optimizations therefore significantly boosting the performance of the web page. In this talk we will provide an introduction to this specification, explaining the types of containment available and the different use cases for each of them. We will also take a look at some examples of optimizations implemented in the rendering engine based on css-contain. Finally, we will review the status of CSS containment on the different browsers and future plans regarding this new feature.