Mislim da ti ova narančasta kapa lijepo stoji.

Mislim is the 1st person singular present of misliti = to think.

So mislim means I think.

The word da introduces a subordinate clause, similar to English that:

• Mislim da... = I think that...

In everyday English, that is often omitted, but in Croatian da is normally kept in this structure.

So the sentence is built like this:

• Mislim = I think
• da ti ova narančasta kapa lijepo stoji = that this orange hat looks good on you / suits you

Ti here is the dative singular form of ti = you (informal singular).

In this sentence, it does not mean you as a subject. It means something like:

• to you
• on you
• for you, depending on the verb

With stajati in the sense of to suit / to look good on someone, Croatian uses the dative:

• Kapa ti stoji lijepo. = The hat looks good on you.
• Ta boja ti dobro stoji. = That color suits you.

So ti is there because Croatian expresses suiting someone with a dative object.

Ova is the feminine singular nominative form of this.

It agrees with kapa, which is:

• feminine
• singular
• here in the nominative, because it is the grammatical subject of stoji

Agreement:

• ovaj = masculine singular
• ova = feminine singular
• ovo = neuter singular

Because kapa is feminine, you need ova:

• ova kapa = this hat

Narančasta is an adjective meaning orange.

Like most Croatian adjectives, it must agree with the noun it describes in:

• gender
• number
• case

Since kapa is feminine singular nominative, the adjective must also be feminine singular nominative:

• narančast = masculine
• narančasta = feminine
• narančasto = neuter

So:

• narančasta kapa = orange hat

Yes, literally stajati often means to stand.

But in this sentence, stajati has an idiomatic meaning:

• to suit
• to look good on someone

So ova narančasta kapa ti lijepo stoji means that the hat looks good on you.

This is a very common Croatian way to talk about clothes, hairstyles, colors, and similar things.

Examples:

• Ta haljina ti dobro stoji. = That dress suits you.
• Kratka kosa joj lijepo stoji. = Short hair looks good on her.

So this is not really about the hat physically standing somewhere.

Because lijepo here is an adverb, not an adjective.

It modifies the verb stoji:

• lijepo = nicely / beautifully / well
• stoji = suits / looks on

So:

• lijepo stoji = looks nice / suits nicely

If you used lijepa, that would be a feminine adjective meaning beautiful, and it would need to describe a noun:

• lijepa kapa = a beautiful hat

But here the idea is not the hat is beautiful. It is the hat looks good on you. That is why Croatian uses the adverb lijepo.

The basic meaning stays the same even if the word order changes, because Croatian word order is fairly flexible.

The sentence you have is natural:

• Mislim da ti ova narančasta kapa lijepo stoji.

You could also hear:

• Mislim da ova narančasta kapa ti lijepo stoji.
• Mislim da ova narančasta kapa lijepo stoji ti. — grammatically possible in some contexts, but much less natural
• Ta ti narančasta kapa lijepo stoji. — a different nuance

Why is ti placed early? Because short unstressed words like ti often appear near the beginning of the clause, in a typical clitic position.

So the given order sounds very natural and idiomatic.

Because Croatian does not need a separate preposition here.

English says:

• It looks good on you.

Croatian expresses that idea through the verb stajati plus the dative:

• Ti stoji dobro.
• literally something like: It stands well to you

That is just how Croatian structures the idea. So the meaning of English on you is built into:

• the verb stajati
• plus the dative pronoun ti

Sometimes yes, but the nuance is different.

• Izgleda dobro = looks good
• Lijepo stoji = suits you / looks good on you

If you say:

• Ova kapa izgleda dobro. = This hat looks good.
  This can mean the hat looks good in general.

If you say:

• Ova kapa ti lijepo stoji. = This hat looks good on you.
  This specifically connects the hat to the person wearing it.

So lijepo stoji is better when you mean it suits you personally.

Yes. Ti is informal singular you.

If you are speaking formally to one person, you would usually use vam (dative of formal/plural vi):

• Mislim da vam ova narančasta kapa lijepo stoji.

That means:

• I think this orange hat looks good on you
  said politely/formally

So compare:

• ti = informal singular
• vam = formal singular or plural

Because in Croatian the thing that suits someone is the grammatical subject.

In this sentence:

• ova narančasta kapa = subject
• stoji = verb
• ti = dative object/experiencer

So Croatian structures it like:

• This orange hat suits you

rather than:

• You look good in this orange hat

English can also use the hat as subject:

• This orange hat looks good on you

So the Croatian structure is actually quite close to that English version.

Yes.

• Mislim da ti narančasta kapa lijepo stoji.

That would mean I think the/an orange hat looks good on you, depending on context.

Adding ova makes it more specific:

• ova narančasta kapa = this orange hat

So ova points to a particular hat, probably one you can see or one already mentioned.

A very natural change would be:

• Mislim da ti ova narančasta kapa jako lijepo stoji.

or

• Mislim da ti ova narančasta kapa baš lijepo stoji.

Nuance:

• jako lijepo = very nicely / very well
• baš lijepo = really nicely / especially well

So Croatian often strengthens lijepo stoji with adverbs like jako or baš.