php正则表达式preg_match获取css类，id和标签

I have following css code

thead 
{
    /*some code*/
}
tr,img {
    /*some code*/
}
@page {
    /*some code*/
}
p,h2,h3 {
    /*some code*/
}
h2,h3 {
    /*some code*/
}
img {
    /*some code*/
}

I want all css related to img using php regular expression preg_match or preg_replace. For example if I searched for img, following output will have to show

tr,img {
    /*some code*/
}
img {
    /*some code*/
}

php code is

$str='img{  } .class_class { } #awesome_id{ }';
$search='img';
$str = preg_replace("~{(."$search".)}~s","", $str);
$arr = array_filter(explode(' ',$str));
print_r($arr);

You can use this code:

$re = '/.*\bimg\b.*?{(?s:.*?)}/i'; 
$str = "thead 
{
    /*some code*/
}
tr,img {
    /*some code*/
}
@page {
    /*some code*/
}
p,h2,h3 {
    /*some code*/
}
h2,h3 {
    /*some code*/
}
img {
    /*some code*/
}"; 
preg_match_all($re, $str, $matches);

Here is a regex demo

Explanation:

• .* - matches any characters but a newline, 0 or more times before
• \bimg\b - a literal whole word img (case-insensitively due to i flag)
• .*? - any characters but a newline, 0 or more but as few as possible
• { - a literal {
• (?s:.*?) - any character even a newline (due to (?s:) inline flag) but as few as possible
• } - Literal }.