There are allready tipps out there how to make illuminated buttons
but i like to show how i made them.
This are "Ink Cups" from tattoo machines.
They are very cheap (100pcs about 2-3$) and available in different sizes.
I filled them about 4 mm with hot clue.
The LEDs are bended above tacticle buttons like this way.
Now use a soldering iron with an old soldering tip
to head up the center part a little bit (about 1mm deep) and put the cup on the LED.