Sve što želim večeras jest miran san.

Sve što is a very common pattern meaning everything that or all that.

So:

• sve = everything / all
• što = that / what

Together, sve što želim večeras means everything that I want tonight or more naturally in English, all I want tonight.

This is one of the most useful relative-clause patterns in Croatian.

Here, što is not a question word. It is a relative pronoun.

Compare:

• Što želiš? = What do you want?
  Here što is interrogative.

• Sve što želim... = Everything that I want...
  Here što is relative.

In this sentence, što refers to the thing being wanted. It is the object of želim inside the clause što želim večeras.

Because the object of želim is already represented by što.

Structure:

• Sve = everything
• što želim večeras = that I want tonight
• jest miran san = is a peaceful sleep

So the sentence is really:

[Everything that I want tonight] [is] [a peaceful sleep].

That means miran san is not directly attached to želim. It is the complement after jest.

A simpler comparison:

• Želim miran san. = I want a peaceful sleep.
  Here miran san is directly the object.

• Sve što želim večeras jest miran san.
  Here što fills that object role inside the relative clause.

Jest is the full, non-clitic form of the verb biti in the 3rd person singular: is.

In everyday Croatian, people usually say je:

• Sve što želim večeras je miran san.

That is completely natural.

Jest sounds a bit more:

• formal
• emphatic
• literary
• careful

It is often used when the speaker wants the sentence to sound more weighty or neatly balanced.

So:

• je = normal everyday is
• jest = fuller, more emphatic is

Both are correct here.

Yes, but with a small stylistic note.

The sentence itself is natural, but jest makes it sound slightly more polished or literary. In ordinary conversation, many speakers would more likely say:

Sve što želim večeras je miran san.

So if you use the original version, people will understand you perfectly; it just sounds a little more elevated.

Večeras means tonight or this evening, depending on context.

It is an adverb, not a noun phrase.

Examples:

• Dolazim večeras. = I’m coming tonight.
• Večeras sam umoran. = I’m tired tonight / this evening.

In your sentence, it tells you when the wanting applies:

Sve što želim večeras = All I want tonight

Yes. Croatian word order is fairly flexible.

You can also say:

• Sve što večeras želim jest miran san.
• Večeras sve što želim jest miran san.
• Miran san je sve što želim večeras.

These versions are all understandable, but the focus shifts a little.

For example:

• Sve što želim večeras... puts the time expression later inside the clause.
• Sve što večeras želim... puts a bit more attention on večeras.
• Miran san je sve što želim večeras puts strong focus on miran san.

The original order is smooth and very natural.

This is about the Croatian distinction between short and long adjective forms in masculine singular nominative.

• miran = short form
• mirni = long form

In many contexts, the short form is the more neutral choice, especially when you mean a peaceful sleep in a general, indefinite sense.

So:

• miran san = a peaceful sleep

Mirni san is possible in some contexts, but it can sound more definite, marked, or stylistic. In this sentence, miran san is the expected, natural choice.

For a learner, the safest takeaway is:

• after many masculine nouns, the short adjective form is very common in this kind of neutral statement.

Syntactically, it is best understood as the predicate complement after jest.

That means it functions like the noun phrase after to be in English:

• This is a problem.
• All I want is a peaceful sleep.

In Croatian, that complement is commonly in the nominative.

However, the form here does not visibly help much, because with a masculine inanimate noun like san, nominative and accusative look the same:

• nominative: san
• accusative: san

And the adjective also looks the same in the relevant form:

• miran

So even though the form is identical, the function is not the same as a direct object of želim.

Because što želim večeras is a restrictive relative clause: it defines what sve refers to.

Croatian normally does not separate that kind of clause with a comma.

So:

• sve što želim večeras is one connected unit

A comma would usually feel wrong here.

This is similar to English not putting a comma in:

• Everything that I want tonight is a peaceful sleep.

Yes. You could say:

Ono što želim večeras jest miran san.

That is also very natural.

The difference is slight:

• ono što = what / the thing that
• sve što = everything that / all that

In this sentence:

• Ono što želim večeras... = What I want tonight...
• Sve što želim večeras... = All I want tonight...

So sve što adds a little sense of that’s the only thing I want.

Yes, it is very normal Croatian.

It means:

• peaceful sleep
• restful sleep

It sounds natural and idiomatic, not like a word-for-word translation. Croatian often uses san in this way, just as English uses sleep in expressions like a good night’s sleep or peaceful sleep.

So the whole sentence sounds very natural in meaning: the speaker wants nothing complicated, just rest.