The contain CSS property indicates that an element and its contents are, as much as possible, independent from the rest of the document tree.
Containment enables isolating a subsection of the Dom, providing performance benefits by limiting calculations of layout, style, paint, size, or any combination to a Dom subtree rather than the entire page. Containment can also be used to scope CSS counters and quotes....isolating a subsection of the DOM, providing performance benefits...size, or any combination to a DOM subtree rather than the entire...