Combine css selectors with the same properties, php

I'm looking for a PHP library(script) that will be able to combine CSS selectors with the same properties. Here is what I mean:

.myclass{
    font-size: 14px;
    color: red;
}
.something{
    font-size: 14px;
    color: red;
}

After processing the CSS above the result should be:

.myclass, .something{
    font-size: 14px;
    color: red;
}

Any help is appreciated.