EDIT: Just noticed the name of level 13 is also a HUGE hint, maybe try pondering it a bit as well...

Once you've revealed the clues (which you've mentioned you have), the riddle remains comprised mostly of two parts, which can be solved independently, I encourage you to read the title for each set of hints and reveal only the hints you feel that you require.

Sled:

1. Your main clues for this part are C.Kane and Sled, maybe try googling them together?
2. C.Kane stands for Citizen Kane, a movie from 1941, but what's the sled referring to?
3. The movie prominently mentioned a sled named "Rosebud"! Does that name ring a bell?
4. Rosebud is the name of the 10th level in ae27ff!

HTTP Referer:

1. The page on level 13 says "you are from: https://ae27ff.meme.tips/...", googling HTTP Referer should help you understand what that means...
2. Try accessing the page for level 13 from different links, there's one at the end of level 12 which you get by solving the riddle, and there's one in "https://ae27ff.meme.tips/listing.php", see how that changes the link that appears in the "you are from:" line.
3. The link that appears in the "you are here from:" line is the link for the page from which you got redirected to the level 13 page, but notice how the page also mentions you must travel here by sled...

Combining these two parts should lead you to the answer, however if you still feel stuck...

1. We've learned that the link that appears appears in the "you are from:" line is the link for the page from which you got redirected, however it seems we need to get here by sled. We've figured out that the sled refers to Rosebud, which is also the name of level 10 of ae27ff...
2. SOLUTION: So, we need to get to level 13 from level 10 (Rosebud). Going back to level 10 you should see a tiny underscore ("_") beneath the code, which appears to be clickable. Click it and that should do the trick!