learningequality · rtibbles · Jul 5, 2026 · Nov 7, 2025
diff --git a/ricecooker/utils/downloader.py b/ricecooker/utils/downloader.py
@@ -252,6 +252,16 @@ def make_request(
 
 _CSS_URL_RE = re.compile(r"url\(['\"]?(.*?)['\"]?\)")
 
+# Handle CSS imports with a string rather than a url()
+# From MDN docs on @import:
+# https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@import
+# url - Is a <string> or a <url> type representing the location of the resource to import.
+#       The URL may be absolute or relative.
+# Note that this regex is for the specialized import case that can be given a regular
+# string with a URL in it. An @import given a value of type <url>, will be handled
+# by the above regex and associated code.
+_CSS_IMPORT_RE = re.compile(r"@import\s*['\"](.*?)['\"]")
+
 
 # TODO(davidhu): Use MD5 hash of URL (ideally file) instead.
 def _derive_filename(url):
@@ -443,12 +453,18 @@ def css_content_middleware(content, url, **kwargs):
 
         root_parts = urlparse(url)
 
+        def repl_url(match):
+            return "url(%s)" % fix_url(match)
+
+        def repl_import(match):
+            return "@import%s" % fix_url(match)
+
         # Download linked fonts and images
-        def repl(match):
+        def fix_url(match):
             src = match.group(1)
 
             if src.startswith("//localhost"):
-                return "url()"
+                return ""
             # Don't download data: files
             if src.startswith("data:"):
                 return match.group(0)
@@ -470,7 +486,7 @@ def repl(match):
 
             if _is_blacklisted(src_url, url_blacklist):
                 print("        Skipping downloading blacklisted url", src_url)
-                return "url()"
+                return ""
 
             derived_filename = derive_filename(src_url)
 
@@ -497,9 +513,10 @@ def repl(match):
                 LOGGER.debug(
                     "Resource already downloaded, skipping: {}".format(src_url)
                 )
-            return 'url("%s")' % new_url
+            return '"%s"' % new_url
 
-        return _CSS_URL_RE.sub(repl, content)
+        urls_rewritten = _CSS_URL_RE.sub(repl_url, content)
+        return _CSS_IMPORT_RE.sub(repl_import, urls_rewritten)
 
     if link_policy is not None and "blacklist" in link_policy:
         url_blacklist += link_policy["blacklist"]

diff --git a/tests/test_downloader.py b/tests/test_downloader.py
@@ -171,3 +171,67 @@ def test_pretextbook_css_fetch():
             / "material_symbols.woff"
         )
         assert font_path.stat().st_size > 0
+
+
+class _FakeResponse:
+    """Minimal requests.Response stand-in for an injected request_fn."""
+
+    def __init__(self, body, content_type="text/css"):
+        self.content = body.encode("utf-8") if isinstance(body, str) else body
+        self.headers = {"content-type": content_type}
+        self.status_code = 200
+        self.encoding = "utf-8"
+        self.url = None
+
+    @property
+    def text(self):
+        return self.content.decode(self.encoding or "utf-8")
+
+    def raise_for_status(self):
+        pass
+
+
+def test_css_import_bare_string_is_archived():
+    """A CSS @import written as a bare string is downloaded and rewritten.
+
+    ``@import "theme.css"`` references a stylesheet the same way
+    ``@import url("theme.css")`` does, but the rewriter only recognised the
+    ``url()`` form, so a bare-string import was neither downloaded nor relinked.
+    """
+    page_url = "https://example.org/index.html"
+    bodies = {
+        "https://example.org/main.css": '@import "theme.css";\nbody { color: red; }',
+        "https://example.org/theme.css": "h1 { color: blue; }",
+    }
+
+    def fake_request(url):
+        return _FakeResponse(bodies[url])
+
+    html = '<html><head><link rel="stylesheet" href="main.css"/></head></html>'
+
+    with tempfile.TemporaryDirectory() as download_root:
+        resource_urls = {}
+
+        def derive_filename(url):
+            return downloader.get_archive_filename(
+                url, page_url, download_root, resource_urls
+            )
+
+        downloader.download_static_assets(
+            html,
+            download_root,
+            "https://example.org/",
+            request_fn=fake_request,
+            derive_filename=derive_filename,
+            resource_urls=resource_urls,
+            relative_links=True,
+        )
+
+        root = Path(download_root)
+        # The imported stylesheet is downloaded to its archive path...
+        assert (root / "example.org" / "theme.css").is_file()
+        # ...and the @import in main.css now points at the local copy, not the
+        # original remote URL.
+        main_css = (root / "example.org" / "main.css").read_text()
+        assert "theme.css" in main_css
+        assert "https://example.org/theme.css" not in main_css