docs: fix missing references (#2163)

Author: sy-records

Diff for: docs/configuration.md

@@ -838,13 +838,13 @@ For more details, see [#1131](https://github.com/docsifyjs/docsify/issues/1131).
 
 > **Warning** Deprecated. Use the CSS var `--theme-color` in your `<style>` sheet. Example:
 >
-```html
-<style>
-   :root {
-     --theme-color: deeppink;
-   }
-</style>
-```
+> ```html
+> <style>
+>   :root {
+>     --theme-color: deeppink;
+>   }
+> </style>
+> ```
 
 - Type: `String`