Installing chromium theme on Avast Secure Browser?

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I just switched from Chrome to Avast Secure Browser as my default browser and so far the only thing I am missing is my fancy dark theme on Chrome (which also works on Chromium). I cannot install it from the chrome web store as it gives an error and when I try to manually copy the extension folder from the chrome appdata folder to the avast secure browser appdata folder I get an access denied error in windows... I guess this is all for security reasons but is there any way to install themes on this browser? I am REALLY partial to black/dark themes on just about all my software.

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I work in very dark spaces, mostly inside the sound booths of live music clubs, and I had previously set all my applications as dark as possible to avoid unnecessary time adjusting my eyes when i look back and forth from my laptop to the mixer to the stage. If you guys could allow themes that would be great! If it's too great a security threat I suppose it can't be helped, but I'd like to know if it's possible!