[Home](./index.md) > [puppeteer](./puppeteer.md) > [Protocol](./puppeteer.protocol.md) > [CSS](./puppeteer.protocol.css.md) > [CSSStyleSheetHeader](./puppeteer.protocol.css.cssstylesheetheader.md) > [isMutable](./puppeteer.protocol.css.cssstylesheetheader.ismutable.md) ## Protocol.CSS.CSSStyleSheetHeader.isMutable property Whether this stylesheet is mutable. Inline stylesheets become mutable after they have been modified via CSSOM API. element's stylesheets are never mutable. Constructed stylesheets (new CSSStyleSheet()) are mutable immediately after creation. Signature: ```typescript isMutable: boolean; ```