Now, this is finally something that actually looks good on mobile, well done!

But I have few nitpicks from what's so far available and not been mentioned already:

1) Header image does not blend well with the background [1].

2) Username info area and topics/comments do not blend well as well. Look at comparison pic between default version and mobile one [2] — I suggest to keep white background as in default forum, so there is no problem of blending between two different colors.

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[1] https://talkimg.com/image/0gzvd
[2] https://talkimg.com/image/0gIN2