Mislim da ti ova plava suknja stvarno dobro stoji.

A natural breakdown is:

• Mislim = I think
• da = that
• ti = to you / you (dative)
• ova = this
• plava = blue
• suknja = skirt
• stvarno = really
• dobro = well
• stoji = stands / suits / looks good

So the literal sense is something like:

I think that this blue skirt really stands well on you.

In natural English, that becomes:

I think this blue skirt really suits you.
or
I think this blue skirt looks really good on you.

After misliti (to think), Croatian normally uses da to introduce the clause that follows.

• Mislim da... = I think that...

This is very common in Croatian. English can sometimes drop that:

• I think this skirt suits you.

Croatian usually keeps da:

• Mislim da ti ova plava suknja dobro stoji.

So da is not optional here in standard usage.

Ti here is the dative singular form of you.

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

• Suknja ti stoji. = The skirt suits you.
• literally: The skirt stands to you.

So:

• ti = to you / on you in this structure

It is not:

• te = accusative
• tebe = stressed accusative/genitive form

This verb pattern simply requires the dative.

Because ti is an unstressed clitic pronoun. In Croatian, clitics usually go in the second position of their clause.

Here the clause is:

• da ti ova plava suknja stvarno dobro stoji

After da, the clitic ti comes very early, before the full noun phrase ova plava suknja.

That is why da ti ova plava suknja... sounds natural.

A learner might want to say:

• Mislim da ova plava suknja ti...

but that is less natural in neutral standard word order.

Yes, the basic meaning of stojati / stajati is to stand. But in this sentence it is being used in a very common extended sense:

• dobro stajati nekome = to suit someone / to look good on someone

So here stoji does not mean that the skirt is physically standing somewhere. It means:

• it looks good on you
• it suits you
• it fits your appearance well

This is a very useful expression for clothes.

The standard verb is stajati, and its 3rd person singular present form is stoji.

So:

• ja stojim / on stoji
• infinitive: stajati

Learners are often confused because the infinitive and present stem look different. That is normal for this verb.

In this sentence:

• stoji = it suits / it looks good

Ova plava suknja is in the nominative feminine singular, because it is the subject of the verb stoji.

All three words agree with each other:

• ova = feminine singular nominative of ovaj (this)
• plava = feminine singular nominative of plav (blue)
• suknja = feminine singular nominative (skirt)

So they match in:

• gender: feminine
• number: singular
• case: nominative

That is why you get:

• ova plava suknja

and not forms like ovu plavu suknju, which would be accusative.

They do slightly different jobs:

• dobro = well
• stvarno = really

So:

• dobro stoji = looks good / suits
• stvarno dobro stoji = really looks good / really suits

In other words, stvarno strengthens the whole idea.

You can think of it as:

• stvarno modifies dobro stoji

Yes. Depending on context, dobro stoji with clothes can suggest:

• it suits you
• it looks good on you
• it fits you well

Often the main idea is visual: the item is flattering on the person. But in real usage, there can be some overlap with fits well.

If you want to focus strictly on physical fit, Croatian may also use other expressions, but dobro ti stoji is very common for clothes looking good on someone.

Only if the meaning is already obvious from context, but normally you keep it because it tells us who the skirt suits.

• Ova plava suknja stvarno dobro stoji.

By itself, that sounds incomplete or odd, because the verb in this sense usually wants the person in the dative.

So normally you would say:

• Ova plava suknja ti stvarno dobro stoji.
• Ova plava suknja joj stvarno dobro stoji.
• Ova plava suknja mi stvarno dobro stoji.

Yes, Croatian word order is flexible, but some orders are more neutral and natural than others.

The sentence you have is a very natural neutral version:

• Mislim da ti ova plava suknja stvarno dobro stoji.

You might also hear variations such as:

• Mislim da ova plava suknja ti stvarno dobro stoji.
• Mislim da ti stvarno dobro stoji ova plava suknja.

These can sound more marked, more emphatic, or more stylistically shaped.

For a learner, the safest pattern is the one in your sentence.

Croatian has no articles like a or the.

Instead, definiteness is often understood from context or shown with words like:

• ova = this
• ta = that
• ona = that over there / that one

So ova plava suknja already clearly means:

• this blue skirt

No separate word for the is needed.

Yes. The difference is in the demonstrative:

• ova = this
• ta = that
• ona = that over there / that one

So:

• ova plava suknja = this blue skirt
• ta plava suknja = that blue skirt

Grammatically they work the same way here.

It is neutral and natural. It sounds like a normal compliment.

• Mislim da... = a soft, polite way to give an opinion
• stvarno dobro stoji = warm and positive

It is suitable in everyday conversation and does not sound overly formal or overly slangy.

So it is a very useful sentence pattern for complimenting someone’s clothes.