feat(utils): allow reuse of existing computed style in isContainingBlock (floating-ui#2980)

Author: jcfranco

.changeset/early-emus-destroy.md

@@ -0,0 +1,5 @@
+---
+"@floating-ui/utils": patch
+---
+
+feat(getContainingBlock): allow `CSSStyleDeclaration` as an argument

packages/utils/src/dom.ts

@@ -68,9 +68,11 @@ export function isTopLayer(element: Element): boolean {
   });
 }
 
-export function isContainingBlock(element: Element): boolean {
+export function isContainingBlock(element: Element): boolean;
+export function isContainingBlock(css: CSSStyleDeclaration): boolean;
+export function isContainingBlock(elementOrCss: Element | CSSStyleDeclaration): boolean {
   const webkit = isWebKit();
-  const css = getComputedStyle(element);
+  const css = isElement(elementOrCss) ? getComputedStyle(elementOrCss) : elementOrCss;
 
   // https://developer.mozilla.org/en-US/docs/Web/CSS/Containing_block#identifying_the_containing_block
   return (