That is interesting. I am not aware of any restrictions that prevent users from editing CSS using a mobile device. Either way, only admins can edit site CSS, so there isn't much anyone else can really do to help. UNless, what you meant was you are having trouble finding the CSS. We could help with that.
Actually, now I can't decide. I originally chose this template, because I wanted each character to be color-coded, but I discarded it since the spaces were too large. I then saw the Love Live one, and I thought it also looked good, but I wasn't sure how to change some parameters without messing it up.
The above CSS is the generic CSS that handles the default appearance of the character infoboxes. To customize the colors for a specific infobox, we need only to change the color values depending on the assigned theme. To do this, you will use CSS such as the following where you will replace "mytheme" with the actual theme name and all of the color codes with the actual colors you want to use.