Remove extra height declarations in CSS; remove block styling from dropdowns

app/assets/stylesheets/framework/contextual-sidebar.scss

@@ -9,12 +9,6 @@
     padding-left: $contextual-sidebar-width;
   }
 
-  // Override position: absolute
-  .right-sidebar {
-    position: fixed;
-    height: calc(100% - #{$header-height});
-  }
-
   .issues-bulk-update.right-sidebar.right-sidebar-expanded .issuable-sidebar-header {
     padding: 10px 0 15px;
   }

app/assets/stylesheets/framework/dropdowns.scss

@@ -214,7 +214,6 @@
 .dropdown-menu,
 .dropdown-menu-nav {
   @include set-invisible;
-  display: block;
   position: absolute;
   width: auto;
   top: 100%;

app/assets/stylesheets/framework/sidebar.scss

@@ -89,12 +89,6 @@
 
 .right-sidebar {
   border-left: 1px solid $border-color;
-  height: calc(100% - #{$header-height});
-
-  &.affix {
-    position: fixed;
-    top: $header-height;
-  }
 }
 
 .with-performance-bar .right-sidebar.affix {

app/assets/stylesheets/pages/issuable.scss

@@ -122,7 +122,7 @@
 }
 
 .right-sidebar {
-  position: absolute;
+  position: fixed;
   top: $header-height;
   bottom: 0;
   right: 0;
@@ -243,7 +243,6 @@
 
   .issuable-sidebar {
     width: calc(100% + 100px);
-    height: 100%;
     overflow-y: scroll;
     overflow-x: hidden;
     -webkit-overflow-scrolling: touch;