Correct code background color

fixes #4746

Author: dragonstyle

src/resources/formats/html/bootstrap/_bootstrap-rules.scss

@@ -884,14 +884,18 @@ pre {
 p code:not(.sourceCode),
 li code:not(.sourceCode),
 td code:not(.sourceCode) {
-  @if variable-exists(code-bg) {
+  @if variable-exists(mono-background-color) {
+    background-color: $mono-background-color;
+  } @else if variable-exists(code-bg) {
     background-color: $code-bg;
   }
 
   @if variable-exists(code-padding) {
     padding: $code-padding;
   } @else if variable-exists(code-bg) {
     padding: 0.2em;
+  } @else if variable-exists(mono-background-color) {
+    padding: 0.2em;
   }
 }