thank you youtube (fix #768)

lib/single-file/single-file-core.js

@@ -725,6 +725,7 @@ class Processor {
 
 	removeDiscardedResources() {
 		this.doc.querySelectorAll("." + util.SINGLE_FILE_UI_ELEMENT_CLASS).forEach(element => element.remove());
+		this.doc.querySelectorAll("button button").forEach(element => element.remove());
 		this.doc.querySelectorAll("meta[http-equiv=refresh], meta[disabled-http-equiv], meta[http-equiv=\"content-security-policy\"]").forEach(element => element.remove());
 		const objectElements = this.doc.querySelectorAll("applet, object[data]:not([type=\"image/svg+xml\"]):not([type=\"image/svg-xml\"]):not([type=\"text/html\"]), embed[src]:not([src*=\".svg\"]):not([src*=\".pdf\"])");
 		this.stats.set("discarded", "objects", objectElements.length);