fix playground dark mode (#119)

Author: Rich-Harris

packages/repl/src/lib/Output/srcdoc/index.html

@@ -51,7 +51,7 @@
 				padding: 0;
 			}
 
-			html.dark {
+			body.dark {
 				color-scheme: dark;
 				--bg-1: hsl(0, 0%, 18%);
 				--bg-2: hsl(0, 0%, 30%);