Make errors in pop menu more obvious

[msbboy]

Screen shot of error after attempting to mine a word.

I recently changed my Anki deck name and when I went to mine I forgot to update my Yomitan settings to reflect this. Naturally this broke my mining workflow but I didn't notice this until I looked at Anki and realized none of my cards were getting added. Yomitan does show an error but I didn't notice it during mining. I think just changing the color to red would do a lot to make errors more obvious.