[clang] [docs] Fix good/bad table rendering when the theme is auto-selected to be dark (PR #230545)

[via cfe-commits]

https://github.com/NeKon69 created https://github.com/llvm/llvm-project/pull/230545

When the system prefers dark mode and Furo is set to follow system-wide preferences (i.e. `auto`), switch to dark-styled table rendering.

Before:
<img width="945" height="370" alt="image" src="https://github.com/user-attachments/assets/e0e33120-52a2-49da-84c3-59a70f3a212b" />

After:
<img width="943" height="377" alt="image" src="https://github.com/user-attachments/assets/60f84107-cc67-49bb-b050-7559c2f81e76" />

Fixes #228952

>From 1aaade8cd4197039a42f6a1365036750611e4af5 Mon Sep 17 00:00:00 2001
From: NeKon69 <nobodqwe at gmail.com>
Date: Fri, 9 Oct 2026 17:32:26 +0300
Subject: [PATCH] Add an override for system-detected dark mode

---
 clang/docs/_static/custom.css | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/clang/docs/_static/custom.css b/clang/docs/_static/custom.css
index d159acd79a3668..a1f167901817fd 100644
--- a/clang/docs/_static/custom.css
+++ b/clang/docs/_static/custom.css
@@ -14,6 +14,15 @@ body[data-theme="dark"] {
   --clang-code-comparison-good-border: #3fb950;
 }
 
+ at media (prefers-color-scheme: dark) {
+  body[data-theme="auto"] {
+    --clang-code-comparison-bad-background: rgba(248, 81, 73, 0.16);
+    --clang-code-comparison-bad-border: #f85149;
+    --clang-code-comparison-good-background: rgba(63, 185, 80, 0.16);
+    --clang-code-comparison-good-border: #3fb950;
+  }
+}
+
 /* Use the full viewport on ordinary desktop displays, where Furo's fixed
    content width leaves little room after both sidebars. Once the content area
    reaches 90em (84em plus padding), grow symmetric outer margins instead. */