Splitting a css file

Question

I have this to split a file into smaller files with 200000 characters each.

$i = 1;
$fp = fopen("styles.css",'r');
while(! feof($fp)) {
    $contents = fread($fp,200000);
    file_put_contents('styles'.$i.'.css',$contents);
    $i++;
}

However, splitting a css file requires more than that. I'll need to have each of them in correct css format. For example:

Original css:

.red {
    color: red;
    font-weight: bold;
    font-size: 15px;
    background: black;
}

.blue {
    color: blue;
}

What might happen:

.red {
    color: red;
    font-weight: bold;
    font-size: 15px;
    background: black;
-------------------split--------------------
}

.blue {
    color: blue;
}

What I expect

.red {
    color: red;
    font-weight: bold;
    font-size: 15px;
    background: black;
}
-------------------split--------------------

.blue {
    color: blue;
}

Is there a way to have PHP split file by number of character, but always make sure that every file ends with "}"? So some file has more than 200000 characters, and some file has less than 200000 characters.

This is not a duplicated question since I want to split file and keep all the pieces, not just cutting a string.