standardize CSS formatting for features code block

The first and last code blocks on this table had the Dark Code Theme button available, and they use a different font than the middle two blocks.

PiperOrigin-RevId: 478562331
Change-Id: I479c520bbaaa0a9f9d261d8d8d6bdb7d12990608

site/en/docs/cc-toolchain-config-reference.md

@@ -156,7 +156,7 @@ support and expansion. These are:
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-   <td><code>implies = ['feature']</code>
+   <td><pre>implies = ['feature']</pre>
    </td>
    <td><p>Feature-level. This feature implies the specified feature(s).
        Enabling a feature also implicitly enables all features implied by it
@@ -167,7 +167,7 @@ support and expansion. These are:
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-   <td><code>provides = ['feature']</code>
+   <td><pre>provides = ['feature']</pre>
    </td>
    <td><p>Feature-level. Indicates that this feature is one of several mutually
        exclusive alternate features. For example, all of the sanitizers could