Thanks Denis, but the issue was not in the question id selector. You were always right about the structure of the id tag selector (#questionQQ). The problem was in the expression used to tag the answer part of the question.
Solution:
1. I used Firefox to inspect the CSS of the generated page (Tools, Web Developer, Inspect). (Firebug (a Firefox plugin), by the way, gave me the wrong tag which was the one used in the previous post. That was the real core of the problem.)
2. The new tag provided by Firefox was: ul.answers-list.radio-list
3. My new code was:
#question163 ul.answers-list.radio-list {
text-align: center;
}It worked perfectly. I was able to target #question163 only (as an ID Tag should do).
Thank you, especially for helping me think through this process.