Fix reading view state for discussion thread listing

lms/static/sass/discussion/elements/_navigation.scss

@@ -207,6 +207,7 @@
 .forum-nav-thread {
   border-bottom: 1px solid $forum-color-border;
   background-color: $forum-color-background;
+  margin-bottom: 0;
 
   &.is-unread {
     background: $forum-color-background;
@@ -226,19 +227,30 @@
 .forum-nav-thread-link {
   display: block;
   padding: ($baseline/4) ($baseline/2);
+  transition: none;
 
-  &.is-active {
-    background-color: $forum-color-background;
-    color: $base-font-color;
+  &.is-active,
+  &:hover {
+    color: $forum-color-background;
+    background-color: $forum-color-hover-thread;
+
+    .forum-nav-thread-labels > li {
+      border-color: $forum-color-background;
+      color: $forum-color-background;
+    }
 
     .forum-nav-thread-comments-count {
-      background-color: $gray-l4;
+      background-color: $forum-color-background;
       color: $base-font-color;
 
       &:after {
         border-right-color: $gray-l4;
       }
     }
+
+    span.icon {
+      color: $forum-color-background;
+    }
   }
 
   .forum-nav-thread-comments-count {

lms/static/sass/discussion/utilities/_variables-v1.scss

@@ -14,6 +14,7 @@ $forum-color-community-ta: $green-d1 !default;
 $forum-color-marked-answer: $green-d1 !default;
 $forum-color-border: $gray-l3 !default;
 $forum-color-error: $red !default;
+$forum-color-hover-thread: $gray-d3 !default;
 
 // post images
 $post-image-dimension: ($baseline*3) !default;  // image size  + margin

lms/static/sass/discussion/utilities/_variables-v2.scss

@@ -14,6 +14,7 @@ $forum-color-community-ta: $green-d1 !default;
 $forum-color-marked-answer: $green-d1 !default;
 $forum-color-border: palette(grayscale, base) !default;
 $forum-color-error: palette(error, accent) !default;
+$forum-color-hover-thread: palette(grayscale, dark) !default;
 
 // post images
 $post-image-dimension: ($baseline*3) !default;  // image size  + margin