style: update nested ol (#22057)

<!--Delete sections as needed -->

## Description

Update style for nested ordered lists to use numbers, then letters, then
roman numerals.

Example:

https://deploy-preview-22057--docsdocker.netlify.app/contribute/components/lists/
https://docs.docker.com/contribute/components/lists/


![image](https://github.com/user-attachments/assets/bdcaf793-e970-402a-8e8a-3c18d5554584)

## Related issues or tickets

<!-- Related issues, pull requests, or Jira tickets -->

## Reviews


- [ ] Editorial review

Signed-off-by: Craig <[email protected]>

Author: craig-osterhout

assets/css/lists.css

@@ -0,0 +1,12 @@
+.prose ol {
+    list-style-type: decimal;
+}
+
+.prose ol ol {
+    list-style-type: lower-alpha;
+}
+
+.prose ol ol ol {
+    list-style-type: lower-roman;
+}
+

assets/css/styles.css

@@ -13,3 +13,4 @@
 @import "/assets/css/syntax-light";
 @import "/assets/css/syntax-dark";
 @import "/assets/css/icons";
+@import "/assets/css/lists";