All the themes available on getpublii are responsive by default so you won’t have to do anything. You can try it when viewing a webpage: just press CTRL + SHIFT + M (on Google Chrome you need to press F12 first) and choose the device that you want (for example iPhone, iPad or Pixel 2 XL).
About your first question: what do you mean by changing the color of the tags? Where are the tags visible? Which theme do you use?
You write that a ‘s’ was missing at the end of a file. If this file was part of a theme you could report it here on the forum as bug?