Fix old docs light mode code background

Author: m-murasovs

apify-docs-theme/src/theme/custom.css

@@ -162,7 +162,7 @@ html[data-theme='dark'] {
     --ifm-footer-link-color: #6b6e80;
     --max-layout-width: 1440px;
 
-    --ifm-code-background: #f6f8fa;
+    --ifm-code-background: var(--ifm-pre-background);
 
     --docusaurus-highlighted-code-line-bg: rgba(0, 0, 0, 0.1);