Fix code blocks in dark mode (#733)

### Prerequisites

Put an `x` into the box(es) that apply:

- [x] This pull request fixes a bug.
- [ ] This pull request adds a feature.
- [ ] This pull request introduces breaking change.

### Description

In dark mode, the `code` tag inside `pre` in source code blocks has a
different background color, resulting in two different colors like the
following example:


![codeblocks](https://user-images.githubusercontent.com/26819407/202913094-757949fa-feb6-43a3-ae01-2a3a9ed6b5ee.png)

The bug seems to have been introduced by commit
476429d42ac1971595ccd44a8232685a5ee86d8a.

I have fixed it by adding `inherit` colors to `code` tags that are
inside `.highlight` classes.

### Issues Resolved

No issue has been filed.

### Checklist

Put an `x` into the box(es) that apply:

#### General

- [x] Describe what changes are being made
- [x] Explain why and how the changes were necessary and implemented
respectively
- [ ] Reference issue with `#<ISSUE_NO>` if applicable

#### Resources

- [x] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

- [ ] Add yourself to `CONTRIBUTORS.md` if you aren't on it already

assets/scss/_base_dark.scss

@@ -43,6 +43,11 @@
     pre {
       background-color: $alt-bg-color-dark;
       color: $fg-color-dark;
+
+      code {
+        background-color: inherit;
+        color: inherit;
+      }
     }
   }
 

resources/_gen/assets/scss/scss/coder-dark.scss_1fcd9040f1144c65015c77e7b93bc5ac.json

@@ -1 +1 @@
-{"Target":"css/coder-dark.min.78b5fe3864945faf5207fb8fe3ab2320d49c3365def0e88ac1df0ddadc54a03c.css","MediaType":"text/css","Data":{"Integrity":"sha256-eLX+OGSUX69SB/uP46sjINScM2Xe8OiKwd8N2txUoDw="}}
+{"Target":"css/coder-dark.min.216e36d3eaf6f4cdfd67dc1200c49a8169e6478102977b3e9ac51a064c57054c.css","MediaType":"text/css","Data":{"Integrity":"sha256-IW420+r29M39Z9wSAMSagWnmR4ECl3s+msUaBkxXBUw="}}