Learn Arabic (Modern Standard): كأن المطعم الباهر ديكوره قصر. - It is as if the restaurant whose decor is dazzling is a palace.

This is the signature of the Causal Adjective (النعت السببي). Instead of directly describing the noun before it, it describes a feature related to it (the decor). However, grammatically, it must still agree with the preceding noun (المطعم) in definiteness and case. Since المطعم is definite and accusative, الباهر is too.

What determines the gender of the causal adjective الباهر here?

Unlike a regular adjective, the causal adjective takes its gender from the noun that comes after it. Here, ديكور is masculine, so الباهر is masculine. If we changed the following noun to a feminine word like إضاءة (lighting), the adjective would become feminine: الباهرة إضاءته.

Why is ديكور in the nominative case (marfu')?

In this structure, the causal adjective الباهر acts almost like a verb meaning 'is dazzling'. The noun following it (ديكور) acts as the subject doing that action. Because subjects take the nominative case, it is pronounced ديكورُ (with a damma).

Why is there a pronoun suffix ـه attached to ديكوره?

The noun following a causal adjective must always contain a pronoun suffix that links it back to the main noun being described. Here, the ـه (its) points back to المطعم (the restaurant), giving us the literal underlying meaning 'the restaurant, dazzling is its decor'.