Adjectival order: “a style appropriate for” or “an appropriate style for”

I would like to understand the correct grammatical order in the sentence,

In your essay, you must use grammatically correct sentences with accurate spelling and punctuation in a style appropriate for the situation.

I hold the view that “style appropriate” is written bad because the grammatical order indicates that an adjective needs to be before the noun.

Is it grammatically correct?: NOUN + ADJECTIVE X

So,

In your essay, you must use grammatically correct sentences with accurate spelling and punctuation in an appropriate style for the situation .

It is true that it works like this ​ ADJECTIVE + NOUN ​

Resource: Cambridge English Objective First Book, Fourth Edition

"Style appropriate for the situation" is not incorrect and not badly written. The placement of multi-word adjective phrases doesn't always follow the same rules as the placement for single-word adjectives.

In English, adjective phrases that contain a prepositional phrase ("for the situation", in this case) aren't placed before the noun: we don't say things like "an appropriate for the situation style". (There may be a few cases where this kind of construction is actually acceptable, but the general rule is as I have given it.) To avoid this, the entire adjective phrase is typically placed after the noun: "a style [appropriate for the situation]".

Sometimes, it is possible to say more or less the same thing by modifying the noun with an adjective before it and a prepositional phrase after it. "An appropriate style for the situation" works: it means the same thing as "a style for the situation that is appropriate". The for-prepositional phrase "for the situation" makes sense either as a modifier of the adjective appropriate or of the noun style.

Sometimes, we can't rephrase like this, because the prepositional phrase only makes sense with the adjective, not with the noun. For example, we can't replace "a heart undaunted by opposition" with *"an undaunted heart by opposition", because "heart by opposition" doesn't make sense.

It's correct because the adjective [style "appropriate"] you used, is a postpositive adjective.

Sometimes an adjective does occur immediately after a noun.

In certain institutionalised expressions:

1. the Governor General
2. the Princess Royal
3. times past

So note that we refer to these as Postpositive adjectives.

Postposition is obligatory when the adjective modifies a pronoun or noun:*

1. style appropriate [your example]
2. something useful
3. everyone present
4. those responsible

Postpositive adjectives are commonly found together with superlative, attributive adjectives:

1. the shortest route possible
2. the worst conditions imaginable
3. the best hotel available