Pre-release: Style Improvements

Improved styles at mobile end (especially for wechat, alipay and mobile qq).

Also, due to iPhone 5 series' low-resolution characteristic, we make the font-size of modal title smaller. From 1 rem to 18px (((it's strange but it works). Make sure everything is ok and looks nice.

Still, this is a pre-release. You know what I mean.jpg