$$\text{BH}_3$$ acts as a Lewis acid whereas $$\text{NH}_3$$ acts as Lewis base. Explain with proper structures?

PLACEHOLDER ANSWER - the answer is an explanation. In $$\text{BH}_3$$, boron is $$sp^2$$ hybridised with a trigonal planar structure, and has only six electrons in its valence shell and an empty p orbital, so it accepts an electron pair and acts as a Lewis acid. In $$\text{NH}_3$$, nitrogen is $$sp^3$$ hybridised with a pyramidal structure and has a lone pair, which it donates, so it acts as a Lewis base. The two combine to form the adduct $$\text{H}_3\text{B} \leftarrow \text{NH}_3$$.