Fix example code block padding for PHP 8.3+

[ElfSundae]

This pull request fixes the missing padding in example code blocks introduced by changes in PHP 8.3+.
Since highlight_string() now returns <pre><code>...</code></pre> instead of <code>...</code>, the existing CSS rule targeting only <code> no longer applied.

The fix adds <pre> to the selector so both cases are covered:

+.docs .example-contents > .phpcode > pre,
 .docs .example-contents > .phpcode > code {
     padding: .75rem;
 }

This ensures that the padding style is correctly applied to all example code blocks.