Wiring for LED bathroom mirror - sanity check please!

[Left Peg]

hi

for the electricians - what’s the best or correct way to wire in a bathroom LED mirror to mains?

my current understanding is that the existing light circuit would be identified, add a pattress box to the light circuit cable, and then run a cable to the LED mirror (Live to Live, Neutral to Neutral, Ground to Ground etc) - is this correct?

additional info - walls are plasterboard and i would need to identify the lighting circuit from the loft and drop a cable down the plasterboard partition to feed the mirror.

thanks!