There is no hard and fast rule on how many pixels space you need to place as it varies. The gap needed between an adsense unit and a button will be larger on a mobile device than on a desktop using a mouse and the requirement is that it needs to be of adequate spacing to prevent inadvertent clicks when trying to click the button or link instead.
The only time Google applies a hard and fast rule on the distance from adsense units is how close they can be to flash game content as a user clicking madly in a flash game could easily come out of the games flash viewport and click on the ads inadvertently.
Basically what it boils down to is can you justify how you came up with the distance, can you honestly say you thought about and have come up with 00px for xyz reason. If you can then you should be in the clear. The main thing is that you should not have clickable content right next to the adsense unit as that could be interpreted as trying to trigger a false click.