Revert "Removed blue background from code examples to improve readability"

This reverts commit 6f61fb2456efcb2a815f6f02f6b207f0303b24b7.
diff --git a/user_guide_src/source/_themes/eldocs/static/asset/css/common.css b/user_guide_src/source/_themes/eldocs/static/asset/css/common.css
index ec6adec..c216c36 100644
--- a/user_guide_src/source/_themes/eldocs/static/asset/css/common.css
+++ b/user_guide_src/source/_themes/eldocs/static/asset/css/common.css
@@ -134,10 +134,6 @@
 	padding: 10px 10px 8px; 
 }
 
-.highlight-ci{
-	background:none;
-}
-
 	.highlight-ci,
 	.highlight-ee,
 	.highlight-rst,