gh-129939: Add darkmode support for difflib's comparison pages (#129940)

Author: Wulian233

Doc/whatsnew/3.14.rst

@@ -411,6 +411,13 @@ decimal
   :meth:`Decimal.from_number() <decimal.Decimal.from_number>`.
   (Contributed by Serhiy Storchaka in :gh:`121798`.)
 
+difflib
+-------
+
+* Comparison pages with highlighted changes generated by the
+  :class:`difflib.HtmlDiff` class now support dark mode.
+  (Contributed by Jiahao Li in :gh:`129939`.)
+
 dis
 ---
 

Lib/difflib.py

@@ -1632,13 +1632,22 @@ def _line_pair_iterator():
 </html>"""
 
 _styles = """
+        :root {color-scheme: light dark}
         table.diff {font-family:Courier; border:medium;}
         .diff_header {background-color:#e0e0e0}
         td.diff_header {text-align:right}
         .diff_next {background-color:#c0c0c0}
-        .diff_add {background-color:#aaffaa}
+        .diff_add {background-color:palegreen}
         .diff_chg {background-color:#ffff77}
-        .diff_sub {background-color:#ffaaaa}"""
+        .diff_sub {background-color:#ffaaaa}
+
+        @media (prefers-color-scheme: dark) {
+            .diff_header {background-color:#666}
+            .diff_next {background-color:#393939}
+            .diff_add {background-color:darkgreen}
+            .diff_chg {background-color:#847415}
+            .diff_sub {background-color:darkred}
+        }"""
 
 _table_template = """
     <table class="diff" id="difflib_chg_%(prefix)s_top"

Lib/test/test_difflib_expect.html

@@ -9,13 +9,22 @@
           content="text/html; charset=utf-8" />
     <title></title>
     <style type="text/css">
+        :root {color-scheme: light dark}
         table.diff {font-family:Courier; border:medium;}
         .diff_header {background-color:#e0e0e0}
         td.diff_header {text-align:right}
         .diff_next {background-color:#c0c0c0}
-        .diff_add {background-color:#aaffaa}
+        .diff_add {background-color:palegreen}
         .diff_chg {background-color:#ffff77}
         .diff_sub {background-color:#ffaaaa}
+
+        @media (prefers-color-scheme: dark) {
+            .diff_header {background-color:#666}
+            .diff_next {background-color:#393939}
+            .diff_add {background-color:darkgreen}
+            .diff_chg {background-color:#847415}
+            .diff_sub {background-color:darkred}
+        }
     </style>
 </head>
 

Misc/NEWS.d/next/Library/2025-02-10-14-34-34.gh-issue-129939.B08L4e.rst

@@ -0,0 +1,2 @@
+Comparison pages with highlighted changes generated by the
+:class:`difflib.HtmlDiff` class now support dark mode.