(Adjective) + 限(かぎ)りだExtremely, Really, Very, As ... as one can be

限(かぎ)りだ is a structure that follows adjectives in order to indicate that something is 'extremely (A)', or 'as (A) as can be'. This grammar pattern is simply a mix of the noun 限(かぎ)り, 'limit', and the auxiliary verb だ, or です in the case of a polite sentence. Therefore, the literal meaning is just that something is 'the limit of (A)', where (A) is some describable feature.

限(かぎ)りだ will follow adjectives in their standard forms.

限(かぎ)りだ is a fairly formal grammar point that simply aims to highlight the intensity of traits as perceived by the speaker. As this perception is something coming from the speaker, the adjective itself will often be an emotion that the speaker themselves is experiencing, rather than a direct quality of the object, such as its color or shape. Some examples of this are as follows.

嬉(うれ)しい - The feeling of happiness, as experienced by the speaker.

頼(たの)もしい - The feeling of reliability, as experienced by the speaker.

羨(うらや)ましい - The feeling of jealousy, as experienced by the speaker.

寂(さみ)しい - The feeling of loneliness, as experienced by the speaker.

恥(はず)ずかしい - The feeling of embarrassment, as experienced by the speaker.

心強(こころづよ)い - The feeling of reassurance, as experienced by the speaker.

As can be seen in all of the examples. The intensity of the adjective is something that will change depending on one speaker to the next, rather than something that the target is doing.