MDL-42692 Quiz: Fixed z-index for tab and marks

On edit quiz page marks/reorder text box has zindex set, which should be considered by modal
window. Also, tab set is also using zindex for active node.

lib/outputrenderers.php

@@ -3134,7 +3134,7 @@ EOD;
             // No name for tabtree root.
         } else if ($tabobject->inactive || $tabobject->activated || ($tabobject->selected && !$tabobject->linkedwhenselected)) {
             // Tab name without a link. The <a> tag is used for styling.
-            $str .= html_writer::tag('a', html_writer::span($tabobject->text), array('class' => 'nolink'));
+            $str .= html_writer::tag('a', html_writer::span($tabobject->text), array('class' => 'nolink moodle-has-zindex'));
         } else {
             // Tab name with a link.
             if (!($tabobject->link instanceof moodle_url)) {

mod/quiz/styles.css

@@ -745,7 +745,6 @@ table#categoryquestions {
     width: 1.4em;
     padding-right: 0.3em;
     padding-left: 0;
-    z-index: 99;
     text-align: right;
     color: #333;
 }
@@ -774,7 +773,6 @@ table#categoryquestions {
     border-radius: 0.2em;
     border-bottom-left-radius: 0;
     border-top-left-radius: 0;
-    z-index: 900;
     display: block;
     margin: 0;
     background-color: #ddf;
@@ -794,7 +792,6 @@ table#categoryquestions {
     border-radius: 0.2em;
     border-bottom-left-radius: 0;
     border-top-left-radius: 0;
-    z-index: 900;
     display: block;
     margin: 0;
     background-color: #ddf;
@@ -838,7 +835,6 @@ table#categoryquestions {
     position: absolute;
     right: 0.3em;
     top: 0;
-    z-index: 900;
     display: block;
     padding: 0.2em;
     background-color: #F9F9F9;
@@ -1048,7 +1044,6 @@ bank window's title is prominent enough*/
     top: 0.2em;
     right: 0.2em;
     display: inline;
-    z-index: 900;
 }
 #page-mod-quiz-edit .quizpagedelete img {
     background-color: #d6d6d6;