Does Silence retroactively remove Daybreak buffs?

I'm assuming that would be why an 8 defense guy would die to 6 damage.

But it's very counter intuitive since daybreak is not a static ability.

(Also, is there a way I can see celestial cards in cards menu?)

Are you talking about Sunburst? Read the full text of the spell and that should explain it (hint: Sunburst Silences the unit before it damages it)

Silence removes ALL TEXT (Any buffs/Keywords/Ephemeral/etc) with the exception of Spellshield.

In the case of Sunburst, The silence happens first (so a unit with extra health loses all buffs) then damage happens after.
In other words, any unit with a base health of 6 or less will die to that spell AS LONG its the first card played on that turn AND the target unit doesn't have Spellshield.

K. I was under the impression that silence only removed text, and not attack / defense buff.