Žao mi je što ti nove sandale ne stoje dobro uz kupaći kostim.

Žao mi je means I’m sorry or I feel sorry/regretful.

Grammatically, it is not built like English I am sorry. It is closer to:

• žao = sorry / regretful / a pity
• mi = to me
• je = is

So the structure is roughly It is sorry to me, which English does not say, but Croatian does.

This is a very common fixed expression:

• Žao mi je. = I’m sorry.
• Žao mi je što... = I’m sorry that...

Here što means that and introduces the clause explaining what the speaker is sorry about:

• Žao mi je što... = I’m sorry that...

So:

• Žao mi je što ti nove sandale ne stoje dobro uz kupaći kostim.
• I’m sorry that your new sandals don’t go well with the swimsuit / don’t suit you well with the swimsuit.

After expressions like žao mi je, što is the normal choice when talking about a real situation or fact.

Ti here is the unstressed dative form of you.

It means to you or, more naturally in English here, on you:

• sandale ti ne stoje dobro = the sandals don’t look good on you / don’t suit you

So ti is not the subject. It is the person affected by how the sandals look.

Not literally.

Ti means to you, not your. But in English, we often translate more naturally with your because the sandals are obviously being discussed in relation to that person.

Compare:

• ti nove sandale ne stoje dobro = the new sandals don’t suit you
• tvoje nove sandale = your new sandals

So if Croatian wanted to state possession explicitly, it could say tvoje nove sandale. In this sentence, possession is not the main grammatical idea; the idea is that the sandals do not look good on you.

Because sandale is a feminine plural noun here, and nove has to agree with it.

So:

• sandale = sandals
• nove sandale = new sandals

Both are:

• feminine
• plural
• nominative here, because nove sandale is the subject of stoje

Agreement is very important in Croatian, so the adjective changes form to match the noun.

Because the subject is plural:

• nove sandale = new sandals

So the verb must also be plural:

• sandale stoje
• not sandale stoji

Here stoje is the present-tense form used with a plural subject.

Yes, the basic meaning of the verb is related to standing, but here it has an extended meaning.

In clothing contexts, stajati can mean:

• to suit someone
• to look good on someone
• to fit someone aesthetically

So:

• Haljina ti dobro stoji. = The dress looks good on you.
• Ove sandale ti ne stoje dobro. = These sandals don’t suit you / don’t look good on you.

So in this sentence, ne stoje dobro means do not look good or do not suit.

Dobro is an adverb meaning well.

It modifies stoje:

• dobro stoje = look good
• ne stoje dobro = do not look good

So the phrase means that the sandals are not a good aesthetic match.

Uz here means with, in the sense of together with or as a match for.

So:

• uz kupaći kostim = with the swimsuit / with the bathing suit

In clothing and style contexts, uz is often used when talking about whether things go together well:

• Ova torba ide uz haljinu. = This bag goes with the dress.
• Sandale ne stoje dobro uz kupaći kostim. = The sandals don’t go well with the swimsuit.

Because uz takes the accusative case.

So kupaći kostim here is accusative singular.

However, since kostim is masculine inanimate, its accusative singular looks the same as the nominative singular. That is why you see:

• nominative: kupaći kostim
• accusative: kupaći kostim

The form does not change, but the case function does.

Also:

• kupaći = bathing / swimming
• kostim = suit

So kupaći kostim means swimsuit or bathing suit.

Croatian word order is more flexible than English word order, but some small words tend to go in an early position in the clause.

In this sentence:

• ti is a clitic, so it normally appears very early
• ne goes directly before the verb

That gives:

• što ti nove sandale ne stoje dobro...

A learner should especially notice:

• ti comes early
• ne stoje is the normal way to negate the verb

Croatian does not usually need the same rigid word order as English, but this order sounds natural and standard.

Yes. For example:

• Žao mi je što tvoje nove sandale ne stoje dobro uz kupaći kostim.

That would explicitly say your new sandals.

But the original sentence is also natural, because Croatian often leaves possession unstated when it is already clear from context, and instead focuses on the person affected:

• ti ... ne stoje dobro = they don’t suit you

So the original version sounds very idiomatic.