Enabling Brave Shields breaks “Sync with system” theme setting on multiple websites.

[Adrian-Samoticha]

Description

When Brave Shields are enabled, websites that offer a “Sync with system” theme setting such that dark mode is automatically enabled if and only if it is enabled on the OS the browser is running on (such as GitHub and YouTube) default to a light theme even when the OS is currently set to dark mode.

Interestingly, YouTube seems to switch to dark mode for a fraction of a second before returning to light mode when dark mode is enabled at an OS level.

I'm aware that blocking websites from accessing OS-related information may help against certain trackers however I believe that if this is intentional, it should be present as an option in the brave-shields panel. Currently, the issue persists despite Brave showing 0 blocked items (on GitHub), which is why I believe this to be a bug.

Steps to Reproduce

1. Open the GitHub website
2. Navigate to the “Appearance” panel in the Settings menu and set the theme to “Sync with system”
3. Enable Brave shields

Actual result:

Expected result:

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave	1.35.103 Chromium: 98.0.4758.102 (Official Build) (arm64)
Revision	273bf7ac8c909cde36982d27f66f3c70846a3718-refs/branch-heads/4758@{#1151}
OS	macOS Version 12.0.1 (Build 21A559)
JavaScript	V8 9.8.177.11
User Agent	Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.102 Safari/537.36
Command Line	/Applications/Brave Browser.app/Contents/MacOS/Brave Browser --disable-client-side-phishing-detection --disable-domain-reliability --enable-dom-distiller --no-pings --component-updater=url-source=https://go-updater.brave.com/extensions --origin-trial-public-key=bYUKPJoPnCxeNvu72j4EmPuK7tr1PAC7SHh8ld9Mw3E=,fMS4mpO6buLQ/QMd+zJmxzty/VQ6B1EUZqoCU04zoRU= --sync-url=https://sync-v2.brave.com/v2 --lso-url=https://no-thanks.invalid --variations-server-url=https://variations.brave.com/seed --variations-insecure-server-url=https://variations.brave.com/seed --flag-switches-begin --flag-switches-end
Executable Path	/Applications/Brave Browser.app/Contents/MacOS/Brave Browser
Profile Path	/Users/adriansamoticha/Library/Application Support/BraveSoftware/Brave-Browser/Default
Linker	lld
Variations	AdRewardsStudy:NextPaymentDayAdServingStudy:MaximumAdNotificationsPerDay=100/MaximumInlineContentAdsPerHour=8/MaximumInlineContentAdsPerDay=40BraveAds.FrequencyCappingStudy:ExcludeAdIfWithinTimeWindow=0hBraveAds.UserActivityStudy:Triggers=EMPTY/Threshold=0.0/IdleTimeThreshold=5BraveDebounceStudy:EnabledConversionsStudy:NewDefaultPatternDefault1pBlockingStudy:DisabledEphemeralStorageStudy:EnabledForceDisableBlinkFeatures:EnabledMacCoreLocationBackendStudy:EnabledNativeCosmeticFilteringStudy:EnabledNavigationThreadingOptimizationsCompat:DisabledPartitionBlinkMemoryCacheStudy:EnabledPartitionConnectionsByNetworkIsolationKeyStudy:EnabledPermissionLifetimeReleaseStudy:EnabledRequestAdsEnabledApiStudy:EnabledSpeedreaderReleaseStudy:Enabled

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes.
• Can you reproduce this issue with the beta channel? n/a
• Can you reproduce this issue with the nightly channel? n/a

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? Obviously, yes.
• Does the issue resolve itself when disabling Brave Rewards? No.
• Is the issue reproducible on the latest version of Chrome? n/a

Miscellaneous Information:

n/a

[rebron]

@Adrian-Samoticha I'm not able to reproduce this. Can you make sure brave://settings/appearance Brave Colors is set to Same as macOS and github is set properly, e.g. Day Theme is dark. With the github example, when I switch light and dark them from system settings, everything goes light or dark them the browser and the content.

[ryanbr]

Which shields settings exactly is causing it? is there any extensions being used also? @Adrian-Samoticha

[rebron]

@Adrian-Samoticha Do you have an extension possibly in conflict here. You can see below, looks like it's working properly.

Screen.Recording.2022-02-25.at.1.39.52.PM.mov

[Adrian-Samoticha]

I have done further research and came to the conclusion that this issue is caused by the fingerprinting setting being set to “strict, may break sites”. Setting it to “standard” appears to fix the issue.

This intuitively makes sense, since the OS dark mode setting can indeed be used for tracking purposes, though what's suspicious is the fact that there's a zero being displayed next to the fingerprinting setting, which implies that no fingerprinting-related items have been blocked for this particular site, even though the setting very much had a visible effect on the way the site works:

What does the zero actually mean? Is it really supposed to represent the number of blocked fingerprinting-related items or does it mean something else entirely?

[nastavoi]

Try to set this flag to disabled. Github, google etc. should then detect system theme just fine when strict fingerprinting is enabled.
#brave-dark-mode-block

It was added sometime ago in brave/brave-core#9735

[Adrian-Samoticha]

Try to set this flag to disabled. Github, google etc. should then detect system theme just fine when strict fingerprinting is enabled. #brave-dark-mode-block

It was added sometime ago in brave/brave-core#9735

Thanks, this actually did the trick.

[ShivanKaul]

What does the zero actually mean? Is it really supposed to represent the number of blocked fingerprinting-related items or does it mean something else entirely?

It represents the number of times Shields blocked something (tracker, ad, etc) on the page that was on a filter list such as EasyList or EasyPrivacy.

As @nastavoi said, #brave-dark-mode-block flag can be used when you want to use Strict mode but still want the website to be able to detect your Dark/Light mode setting.