Перед свадьбой ей долго поправляли брови, потому что одна бровь выглядела темнее другой.

Because the preposition перед meaning before takes the instrumental case when it refers to time or position.

So:

• свадьба = wedding
• перед свадьбой = before the wedding

This is a fixed pattern you should learn:

• перед уроком = before the lesson
• перед работой = before work
• перед встречей = before the meeting

So перед свадьбой is completely regular.

Ей is the dative singular form of она.

• она = she
• ей = to her / for her

In this sentence, ей долго поправляли брови literally means something like they were adjusting her eyebrows for a long time or her eyebrows were being worked on for a long time.

The person receiving the action is often put in the dative in Russian, especially in sentences like:

• Мне помыли голову = They washed my hair
• Ему лечили зуб = They treated his tooth
• Ей поправляли брови = They were touching up her eyebrows

So ей does not mean she is doing the action. It means the action is being done to/for her.

This is a very common Russian pattern: 3rd person plural with no stated subject can mean people / someone / they in a general sense.

So ей долго поправляли брови does not necessarily mean several specific people were doing it. It often just means:

• they were fixing her eyebrows
• someone was touching up her eyebrows
• her eyebrows were being adjusted

Russian often uses this structure where English might use:

• an unspecified they
• someone
• or even a passive construction

Examples:

• Мне сказали = I was told / They told me
• Его пригласили = He was invited
• Ей поправляли брови = Her eyebrows were being touched up / They were touching up her eyebrows

Поправляли is imperfective past plural. The imperfective is used here because the sentence focuses on the process/duration of the action.

That fits well with долго = for a long time.

So:

• долго поправляли = they kept adjusting / were adjusting for a long time

If you used a perfective verb, it would sound more like a completed single result, not the ongoing process.

Compare:

• ей долго поправляли брови = they were touching up her eyebrows for a long time
• ей поправили брови = they fixed/touched up her eyebrows

The first stresses duration; the second stresses completion.

Literally, поправлять means to correct, straighten, adjust, fix up, touch up.

With брови, it usually means something like:

• shaping them
• adjusting their appearance
• evening them out
• touching up makeup
• correcting the eyebrow line

So in this sentence, it suggests cosmetic work before the wedding, not physically moving the eyebrows around.

A natural English translation would often be:

• They spent a long time touching up her eyebrows
• Her eyebrows were adjusted for a long time
• They worked on her eyebrows for a long time

Because the sentence first talks about the eyebrows as a pair, and then it specifies one eyebrow in contrast to the other.

So:

• брови = eyebrows
• одна бровь = one eyebrow
• другой = the other one

This is very natural in both Russian and English:

• They were fixing her eyebrows because one eyebrow looked darker than the other.

First the pair is mentioned, then the problem with one individual eyebrow is explained.

Because бровь is a feminine singular noun.

So everything agreeing with it must also be feminine singular:

• одна = one (feminine)
• бровь = eyebrow
• выглядела = looked (feminine past)

Compare agreement:

• один глаз выглядел = one eye looked
• одно ухо выглядело = one ear looked
• одна бровь выглядела = one eyebrow looked

The ending -а in выглядела shows feminine past tense.

Here другой is in the genitive singular feminine.

After a comparative like темнее = darker, Russian often uses the thing being compared in the genitive:

• выше брата = taller than brother
• старше сестры = older than sister
• темнее другой = darker than the other one

Since бровь is feminine, другой here means of the other eyebrow.

So literally:

• одна бровь выглядела темнее другой = one eyebrow looked darker than the other

This is a standard comparative structure.

Yes. Russian can compare in two common ways:

1. Comparative + genitive

   • темнее другой

2. Comparative + чем

   • темнее, чем другая

Both are correct.

In this sentence, темнее другой is a little more compact and elegant. It is very natural in written and spoken Russian.

So:

• одна бровь выглядела темнее другой
• одна бровь выглядела темнее, чем другая

Both mean the same thing.

Russian has no articles like a and the.

So meanings like a wedding, the wedding, an eyebrow, the other eyebrow are understood from context.

Here:

• одна бровь = one eyebrow
• другой = the other one / another one, depending on context

Because there are two eyebrows, другой is naturally understood as the other eyebrow.

Потому что means because.

It introduces the reason:

• Перед свадьбой ей долго поправляли брови
  = Before the wedding, they spent a long time touching up her eyebrows

• потому что одна бровь выглядела темнее другой
  = because one eyebrow looked darker than the other

So the second clause explains why they were working on her eyebrows for so long.

The word order is natural, but Russian is more flexible than English.

This version:

• Перед свадьбой ей долго поправляли брови, потому что одна бровь выглядела темнее другой.

puts the time expression first, which sets the scene: Before the wedding...

You could rearrange parts of it, but the original sounds very natural and clear.

For example:

• Ей долго поправляли брови перед свадьбой...
• Брови ей долго поправляли перед свадьбой...

These are possible, but they shift emphasis slightly.

The original order is good because it starts with the occasion and context.

Выглядела is past tense, feminine singular, from выглядеть = to look / to appear.

It is used because the whole sentence describes a past situation:

• before the wedding
• they were adjusting her eyebrows
• one eyebrow looked darker than the other

So both actions are presented as part of the same past scene.

Also, выглядеть is often used in Russian exactly like English look in sentences about appearance:

• Она выглядела уставшей = She looked tired
• Дом выглядел старым = The house looked old
• Одна бровь выглядела темнее другой = One eyebrow looked darker than the other

Here долго means for a long time.

It modifies the verb поправляли and tells you about the duration of the process:

• ей долго поправляли брови = they spent a long time adjusting her eyebrows

In other contexts, долго can also mean long in the sense of a long while, but in this sentence the idea is clearly duration.

Common examples:

• Я долго ждал = I waited a long time
• Мы долго говорили = We talked for a long time
• Ей долго поправляли брови = They spent a long time touching up her eyebrows