1. If you look at the grid question with answers, the last column, the right one, where the answers are is centered. This is ugly and makes no sense. However, if you add to /com_communityquiz/templates/default/css/quiz.css

#quiz-reports .grid tbody td:last-child{text-align: left;}

then the last column will be flushed left while keeping the rest of the table centered.

2. line 8 in /com_communityquiz/templates/default/css/quiz.css

.navigation a, .navigation a:link, .navigation a:visited, .navigation a:hover, .navigation a:active{color: #fff;}

overrides JQuery UI which makes some of the buttons unreadable.
You should not specify color for the button text at all. Let the JQueryUI or the template set the color.