how to modify parsed css?

[aloksharma1]

hi,
i have a requirement where i want to modify the parsed css and then replace it in style tag,
for example:

<style id="customCss">
.someClass {
  margin : 20px;  
}
@media (max-width: 600px) {
  .someClass {
  margin : 5px;  
}
}
</style>

i want to parse rule without media query, and modify it and then replace it back in style tag, how to achieve that?

basically i want this to turn into following output:

<style id="customCss">
.someClass {
  margin : 10px;  
  padding:5px;
}
@media (max-width: 600px) {
  .someClass {
  margin : 5px;  
  padding:0;
}
}
</style>