Den gröna mattan passar bra ihop med de vita gardinerna.

Yes, in a way it is — and that is normal in Swedish.

This is called double definiteness. When a noun is definite and has an adjective before it, Swedish usually marks definiteness twice:

• with a separate article: den / det / de
• and with a definite ending on the noun

So:

• den gröna mattan = the green carpet
• de vita gardinerna = the white curtains

Compare:

• en grön matta = a green carpet
• den gröna mattan = the green carpet

This is one of the most important patterns to get used to in Swedish.

Because adjectives usually take -a in two very common situations:

1. after a definite article

   • den gröna mattan
   • de vita gardinerna

2. with plural nouns

   • vita gardiner

So in this sentence:

• gröna is -a because mattan is definite: den gröna mattan
• vita is -a because gardinerna is both plural and definite: de vita gardinerna

Compare:

• en grön matta = an indefinite singular common-gender noun
• den gröna mattan = definite
• vita gardiner = plural
• de vita gardinerna = plural definite

The base forms are:

• matta = rug, carpet
• gardin = curtain

The forms in the sentence are definite forms:

• matta → mattan = the carpet
• gardin → gardiner = curtains
• gardinerna = the curtains

So you can break them down like this:

• matta
  • -n → mattan
• gardin
  • -er → gardiner
• gardiner
  • -na → gardinerna

Because gardinerna is plural.

Swedish definite articles agree like this:

• den for common-gender singular nouns
• det for neuter singular nouns
• de for plural nouns

So:

• den gröna mattan = singular
• de vita gardinerna = plural

Even though gardin is a common-gender noun in the singular, once it becomes plural, the article is de.

Here passar means something like:

• suits
• goes well with
• matches
• fits well with

The verb is passa, and passar is the present tense.

So:

• passa = to suit / to fit / to go well with
• passar = suits / fits / goes well with

In this sentence, it is not about physical size. It is about style, appearance, or compatibility.

Ihop med makes the idea of matching more explicit. It gives the sense of together with or in combination with.

So:

• passar med can sometimes be understood
• passar ihop med is more idiomatic when talking about things that look good together

In other words, ihop med helps express the idea that the carpet and curtains form a good combination.

You can think of passa ihop med as a common expression meaning to go well together with.

Bra means well here, so it is modifying the verb phrase.

• passar = goes / matches / fits
• passar bra = goes well / matches well

So:

• Den gröna mattan passar ihop med de vita gardinerna. = The green carpet goes together with the white curtains.
• Den gröna mattan passar bra ihop med de vita gardinerna. = The green carpet goes well together with the white curtains.

Bra is very common and does not change form here.

Because Swedish main clauses follow the V2 rule: the finite verb normally comes in the second position.

In this sentence:

• Den gröna mattan = first element
• passar = second element

So the sentence is perfectly normal Swedish word order.

This becomes easier to see if you move something else to the front:

• I vardagsrummet passar den gröna mattan bra ihop med de vita gardinerna.

Here I vardagsrummet is now first, so passar still has to stay second.

This verb-second pattern is one of the biggest differences from English.

Yes, but it means something slightly different.

• Den gröna mattan passar bra ihop med de vita gardinerna = you are talking about specific items
• En grön matta passar bra ihop med vita gardiner = you are speaking more generally, like a general design idea

So the original sentence sounds like there is a particular green carpet and particular white curtains being discussed.

In careful reading, de may be pronounced something like de.

But in everyday spoken Swedish, many speakers pronounce both de and dem as dom.

So although the sentence is written:

• de vita gardinerna

in normal speech you will often hear something like:

• dom vita gardinerna

That is very common in spoken Swedish.

Yes — that is a very good idea.

It is useful to learn these parts together:

• passa med
• passa ihop
• passa ihop med
• passa bra ihop med

The full chunk passar bra ihop med is especially useful for talking about:

• clothes
• colors
• furniture
• decoration
• design choices

For example:

• Den här tröjan passar bra ihop med jeans.
• Blått passar bra ihop med vitt.

Learning it as one unit will make it easier to use naturally.