updated readme.md

README.md

@@ -225,12 +225,22 @@ theme:
 It is also possible to use a custom css file by providing the path to the file:
 </p>
 
+#### JSON
+
 ```json
 "theme": {
   "custom_css": "/path/to/custom.css"
 }
 ```
 
+#### YAML
+
+```yml
+theme:
+  custom_css: "/path/to/custom.css"
+```
+
+
 <p align="justify">
 Keep in mind, even if you provide a custom css file, the background and foreground colors will still be applied as long as you provide the correct templating keys in your custom css file like so:
 </p>