fix(theme-live-codeblock): fix live editor border-radius (#10689)

Author: slorber

packages/docusaurus-theme-live-codeblock/src/theme/Playground/styles.module.css

@@ -34,6 +34,10 @@
   direction: ltr;
 }
 
+.playgroundEditor pre {
+  border-radius: 0;
+}
+
 .playgroundPreview {
   padding: 1rem;
   background-color: var(--ifm-pre-background);