New features in Win11: How a black border appears when you select a file or folder in Explorer

In Windows 11, a recent update has caused a black border to appear when selecting files or folders in File Explorer.

In addition, the text color of the update date and time displayed on the right side has also become darker.

This is a new feature included in update KB5039302, which was released in preview on 6/25/2024.

Before installing KB5039302, the black borders do not appear when you select files or folders, as shown below.

Installing KB5039302 or later updates will add the functionality.

This makes it easier to see which files or folders are selected when you select them.

However, some users seem to want to go back to the way things were before.

So, this time I compared the differences before and after installing KB5039302 and was able to successfully revert it to its original state.

How the black border appears when you select a file or folder

The black border that appears when you select a file or folder in File Explorer is only available in the Light theme.

In dark theme you won't notice the difference.

After installing KB5039302, the theme-related file "aero.msstyles" in the following folder will be updated.

C:\Windows\Resources\Themes\aero

*Before the update, the file update date and time was "2023/11/10".

The black border appears due to the update of "aero.msstyles".

I was actually able to restore the previous state by reverting "aero.msstyles" to the previous version.

"aero.msstyles" is a system file and cannot be modified using normal methods, so you will need to follow these steps:

Steps to revert to a previous version

1. If you have already installed KB5039302, please uninstall KB5039302 first.

2. Uninstalling KB5039302 will revert "aero.msstyles" to the previous version.

3. Open the following folder:

C:\Windows\Resources\Themes\aero

4. Copy "aero.msstyles" and save it in your downloads folder or somewhere similar.

*It may be easier to understand if you create a folder named "old aero" and save the files in it.

5. Install KB5039302.

6. Open the following folder:

C:\Windows\Resources\Themes\aero

7. Change the permissions for "aero.msstyles".

Change the file owner to Administrators and grant Administrators full control permissions.

8. Rename "aero.msstyles" to something like "aero.msstyles.bak".

9. When changing the name, a warning screen will appear, so click "Yes".

10. When "File access denied" appears, click "Continue".

11. When the "User Account Control" screen appears, click "Yes".

12. Copy the previous version of "aero.msstyles" that you saved earlier into the "aero" folder.

If it is in this state, it's OK.

13. The process of reverting to the previous version is now complete, so please restart your PC to reflect the changes.

*Please be sure to restart the computer. The changes may not be reflected if you start the computer after signing out or shutting down.

Update KB5039302 is a preview release, so I think the next regular update will replace "aero.msstyles" with a new version.

In that case, just follow the same steps and replace it with the previous version of "aero.msstyles".

What to do if you can no longer open folders after installing the update on March 25, 2025 or later

If you replace "aero.msstyles" using the method on this page after installing the update on March 25, 2025 or later, you will no longer be able to open any folders.

I tried reverting Explorer to an older version, but that didn't help.

Perhaps a system update has replaced "aero.msstyles" and caused Explorer to stop working properly.

If you have already replaced "aero.msstyles" and are unable to open the folder, you can restore "aero.msstyles" using the following steps to enable the folder to open.

1. Open a command prompt as administrator, type the following commands and press Enter:

Learn how to open a command prompt

1. Press Windows key + R to open Run.

2. Type "cmd".

3.Shift + Ctrl + Enter Please press.

If you do not need administrator privileges, just press Enter.

4. When the "User Account Control" message appears, click "Yes".

cd /d c:¥windows¥resources¥themes¥aero

2. Next, type the following command and press Enter:

ren aero.msstyles aero.msstyles.old

This command renames the replacement "aero.msstyles" to "aero.msstyles.old".

3. Next, type the following command and press Enter:

ren aero.msstyles.bak aero.msstyles

This command renames the backed up "aero.msstyles.bak" back to "aero.msstyles."

4. Close the command prompt and restart your PC.

Once your PC boots, File Explorer will return to normal and you will be able to open folders.

"システムファイルチェッカーYou can also revert by running " aero.msstyles ", which will replace the "aero.msstyles" itself with the current version.