i mojaneun yeppeujiman jeo chimarangeun jal an eoullyeo.

-는 marks 이 모자 as the topic: as for this hat...

That works well here because the speaker is making a contrast:

• This hat is pretty
• but it does not go well with that skirt

Using -는 can give a slight contrastive feeling, which fits the sentence nicely.

If you said 이 모자가 예쁘지만..., it would be more of a neutral subject-marking statement, and a little less like speaking of this hat...

-지만 means but or although.

It attaches directly to the stem of a verb or adjective:

• 예쁘다 → stem 예쁘-
• 예쁘지만 = is pretty, but...

So 예쁘지만 links the first idea to the second:

• It’s pretty, but...

It is a very common way to connect two clauses in Korean.

Because -지만 is a grammatical ending, not a separate standalone word.

In Korean, many connectors attach directly to the verb or adjective stem:

• 먹지만
• 좋지만
• 예쁘지만

So you should think of 예쁘지만 as one conjugated form, not as two separate words.

저 means that, usually something over there, far from both the speaker and the listener.

Korean has a three-way distinction:

• 이 = this, near the speaker
• 그 = that, near the listener or already mentioned
• 저 = that over there, far from both

So:

• 이 모자 = this hat
• 저 치마 = that skirt over there

치마랑은 breaks down like this:

• 치마 = skirt
• -랑 = with / together with / and
• -은 = topic or contrast marker

So 치마랑은 means something like:

• with the skirt
• or more literally, as for with that skirt

Here, -은 adds contrast:

• the hat may be pretty on its own,
• but with that skirt, it does not match well.

Also note:

• -랑 is casual
• after a noun ending in a consonant, you usually get -이랑
• more formal alternatives are -와/과 or -하고

The -은 adds a contrastive or topical nuance.

Without it:

• 저 치마랑 잘 안 어울려 = it doesn’t go well with that skirt

With it:

• 저 치마랑은 잘 안 어울려 = with that skirt, though, it doesn’t go well

That extra -은 helps highlight the pairing with the skirt as the point of contrast.

어울리다 means:

• to suit
• to go well with
• to match

It is often used for:

• clothes and accessories
• colors
• hairstyles
• people and personalities
• things that fit well together in general

Examples:

• 이 색은 너한테 잘 어울려.
  This color suits you well.
• 검은 신발은 이 바지랑 잘 어울려.
  Black shoes go well with these pants.

In this sentence, it means the hat and skirt do not make a good combination.

This is a very common Korean pattern: 잘 안 + verb.

Here 잘 means well, so:

• 잘 어울려 = goes well together / suits well
• 잘 안 어울려 = does not go well together

In negative sentences, 잘 often stays because the speaker is talking about the quality or degree of the action:

• 잘 몰라요 = I don’t know well / I’m not very familiar
• 잘 안 보여요 = I can’t see well
• 잘 안 어울려 = it doesn’t match well

So this is very natural Korean.

Yes.

• 안 어울려 = it doesn’t suit / it doesn’t match
• 잘 안 어울려 = it doesn’t match well

잘 안 어울려 can sound a little softer or more natural in situations like clothes and styling, because it focuses on the combination being not a good match, rather than sounding completely absolute.

어울려 is the casual/plain spoken style.

The polite version would be:

• 이 모자는 예쁘지만 저 치마랑은 잘 안 어울려요.

So the sentence you have is in an informal style, likely used:

• with friends
• with someone younger
• in casual dialogue

A lot of example sentences in Korean learning materials use this style because it is common in everyday speech.

Because Korean often omits things that are already understood from context.

In:

• 이 모자는 예쁘지만 저 치마랑은 잘 안 어울려

the understood subject of 잘 안 어울려 is still this hat.

So the full idea is basically:

• This hat is pretty, but [this hat] doesn’t go well with that skirt.

Korean usually leaves out repeated nouns when they are obvious.

Yes. You could also say:

• 저 치마와는 잘 안 어울려.
• 저 치마하고는 잘 안 어울려.
• 저 치마랑은 잘 안 어울려.

They are similar in meaning, but the tone changes a bit:

• -와/과: more formal or written
• -하고: common and conversational
• -랑/이랑: casual and very common in speech

So 치마랑은 sounds natural and conversational.

It can feel like either in English, depending on context.

Here, the natural sense is:

• It’s pretty, but it doesn’t go well with that skirt.

So the speaker is not denying that the hat is pretty. They are saying:

• the hat itself looks nice
• however, the combination is not good

That contrast is exactly what -지만 is doing here.