docs: Dark mode screenshots

var/marketing/Makefile

@@ -1,5 +1,5 @@
 updatescreenshots:
-	SCREENSHOT_DIR=screenshots SHOT_WIDTH=1024 SHOT_HEIGHT=680 repo-helper screenshot mainpage-darkop http://localhost:1337/ --width 1024 --height 680 --dark --script resize_viewport.py
+	SCREENSHOT_DIR=screenshots SHOT_WIDTH=1024 SHOT_HEIGHT=680 SHOT_DARK=1 repo-helper screenshot mainpage-darkop http://localhost:1337/ --width 1024 --height 680 --script resize_viewport.py
 	SCREENSHOT_DIR=screenshots SHOT_WIDTH=1024 SHOT_HEIGHT=680 repo-helper screenshot mainpage-laptop http://localhost:1337/ --width 1024 --height 680 --script resize_viewport.py
 	SCREENSHOT_DIR=screenshots SHOT_WIDTH=600 SHOT_HEIGHT=1160 repo-helper screenshot mainpage-phone http://localhost:1337/ --width 600 --height 1160 --script resize_viewport.py
 	repo-common-image-framer

var/marketing/resize_viewport.py

@@ -6,10 +6,19 @@ from selenium.webdriver.support.ui import WebDriverWait
 from repo_helper.screenshot import set_viewport_size
 
 
+def _enable_dark_mode(driver):
+    driver.execute_cdp_cmd(
+        "Emulation.setEmulatedMedia",
+        {"features": [{"name": "prefers-color-scheme", "value": "dark"}]},
+    )
+
+
 def run(driver):
     WebDriverWait(driver, 30).until(
         lambda d: bool(d.find_element(By.TAG_NAME, "body").get_attribute("loaded-dashboard"))
     )
+    if os.environ.get("SHOT_DARK") == "1":
+        _enable_dark_mode(driver)
     width = int(os.environ["SHOT_WIDTH"])
     height = int(os.environ["SHOT_HEIGHT"])
     set_viewport_size(driver, width, height)