404 Error. Cannot load any css on the Shopware backend

I have made clone of the git repository and install shop step by step by instruction. Go to theme folder and run npm i and grunt. Frontend loads almost successfull (cannot load Modernizr). But when I run backend - cannot load any css file. Run on Windows10 + Openserver (PHP 5.6.29 + Apache 2.4)

Which shopware version do you use?
Currently the 5.2.13 has a problem on windows systems, that the backend css can’t be loaded, because of a wrong separator. We will fix this in 5.2.14.
It should be already fixed in the master branch on github: SW-17448 fix enlight loader realpath for windows · shopware/shopware@22696f8 · GitHub

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