select data from internal json in jsonb postgresql

I have the following table structure:

create table system_log
(
    id bigserial primary key,
    details jsonb
);

Data in 'details' column is json with inner json:

{
  "prop1": "value1",
  "prop2": "value2",
  "body": "{\"prop3\": \"value3\"}"
}

How to select data from inner json like 'select details.body.prop3 ...' ?

Having

insert into system_log values (1, 
'{
"prop1":"value1",
"prop2":"value2",
"body":{"prop3":"value3"}
}');

You could query like this

select jsonb_path_query(details ,'$.body.prop3 ') 
from system_log sl; 

Or also use a condition

select jsonb_path_query(details ,'$.body.prop3 ? (@ =="value3")') 
from system_log sl;

Working sample here
and the docs

The "body" stored as string instead of object json.

was:

{
  "prop1": "value1",
  "prop2": "value2",
  "body": "{\"prop3\": \"value3\"}"
}

should be

{
  "prop1": "value1",
  "prop2": "value2",
  "body": {"prop3": "value3"}
}

This is why all other suggested answers returned "NULL" as result.
Thanks for @AdrianKlaver

You should not store JSON documents as strings in other JSON documents. Change "body": "{\"prop3\": \"value3\"}" to "body": {"prop3": "value3"}, and you can normally access the value using details->'body'->>'prop3' or details#>>'{body,prop3}'.

However, if you absolutely have to work with the nested format, you can still get the string of the inner document, convert it to jsonb, and then access properties of that object:

(details ->> 'body')::jsonb ->> 'prop3'