Fix markdown code blocks getting two backgrounds in preview

Fixes #53246

extensions/markdown-language-features/media/markdown.css

@@ -196,18 +196,15 @@ pre code {
 }
 
 
-.vscode-light pre:not(.hljs),
-.vscode-light code > div {
+.vscode-light pre {
 	background-color: rgba(220, 220, 220, 0.4);
 }
 
-.vscode-dark pre:not(.hljs),
-.vscode-dark code > div {
+.vscode-dark pre {
 	background-color: rgba(10, 10, 10, 0.4);
 }
 
-.vscode-high-contrast pre:not(.hljs),
-.vscode-high-contrast code > div {
+.vscode-high-contrast pre {
 	background-color: rgb(0, 0, 0);
 }