Font change to smaller after changing editors

Hello,
I changed the jce editor to insert a video and when I turned it back all the product descriptions had turned to font size 10px. Is there a way I can change the font size to 12px as it was, without changing every single one? I have spent hours but cant do it. I have more than 100 products..I am sending a picture. It is span style. I dont know where to change it. Can you help me?
Thank you
Anna

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