Fix problems with transparency on some macOS computers

stylesheets/_index.scss

@@ -19,7 +19,7 @@
 }
 
 .gutter {
-  background-color: $color-black-008;
+  background-color: $color-black-008-no-tranparency;
   float: left;
   width: 300px;
   .content {

stylesheets/_modules.scss

@@ -1947,7 +1947,7 @@
   cursor: pointer;
 
   &:hover {
-    background-color: $color-black-008;
+    background-color: $color-black-016-no-tranparency;
   }
 }
 
@@ -1957,7 +1957,7 @@
 }
 
 .module-conversation-list-item--is-selected {
-  background-color: $color-black-008;
+  background-color: $color-black-016-no-tranparency;
 }
 
 .module-conversation-list-item__avatar {

stylesheets/_variables.scss

@@ -50,6 +50,8 @@ $color-dark-70: #414347;
 $color-dark-85: #1a1c20;
 $color-black: #000000;
 $color-black-008: rgba($color-black, 0.08);
+$color-black-008-no-tranparency: #ededed;
+$color-black-016-no-tranparency: #d9d9d9;
 $color-black-012: rgba($color-black, 0.12);
 $color-black-02: rgba($color-black, 0.2);
 $color-black-04: rgba($color-black, 0.4);