Css/StyleAggregate.php
protected function moveImportsToStart($content)
    {
        $imports = '';
        $replaceCallback = function ($match) use (&$imports) {
            $imports .= $match[0];
            return '';
        };
        $content = preg_replace_callback('/@import[^;]+;/i', $replaceCallback, $content);
        $content = $imports.$content;
        return $content;
    }
protected function moveImportsToStart($content)
    {
        $imports = '';
        $replaceCallback = function ($match) use (&$imports) {
            $imports .= $match[0];
            return '';
        };
        $content = preg_replace_callback('/@import[^;]+;/i', $replaceCallback, $content);
        $content = $imports.$content;
        return $content;
    }
Moves import rules to the start of the style sheet.