Rune help!

I'm making a rune on lethality for kayn. But theres no leathality on the blue side in the shop. Do you know why? I wanted to swap with attack damage in the blue then I relised in the red side where the attack is it does +0.74 and on the blue side it does +0.28. Why aren't they the same? Please tell me if theres a lethality on the blue side becuase I saw on videos there is but mayby my computer isn't loading it up.
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