Ui improvements (#4815)

* PLT-4369 - Fixing scroll on mobile in the RHS

* PLT-4924 - Fixing file thumbnail UX

webapp/sass/components/_files.scss

@@ -20,11 +20,21 @@
     position: relative;
     width: 120px;
 
+    &:after {
+        @include opacity(0);
+        @include alpha-property(background, $black, .4);
+        content: '';
+        height: 100%;
+        left: 0;
+        opacity: 0;
+        position: absolute;
+        top: 0;
+        width: 100%;
+    }
+
     &:hover {
-        .file-preview__remove {
-            &:after {
-                @include opacity(1);
-            }
+        &:after {
+            @include opacity(1);
         }
     }
 
@@ -56,18 +66,6 @@
     top: 0;
     width: 100%;
 
-    &:after {
-        @include opacity(0);
-        @include alpha-property(background, $black, .4);
-        content: '';
-        height: 100%;
-        left: 0;
-        opacity: 0;
-        position: absolute;
-        top: 0;
-        width: 100%;
-    }
-
     i {
         color: $white;
         cursor: pointer;

webapp/sass/layout/_sidebar-menu.scss

@@ -1,6 +1,7 @@
 @charset 'UTF-8';
 
 .sidebar--menu {
+    -webkit-overflow-scrolling: touch;
     background: #fafafa;
     border-right: $border-gray;
     display: none;

webapp/sass/responsive/_mobile.scss

@@ -47,6 +47,7 @@
 
             > div {
                 &:first-child {
+                    -webkit-overflow-scrolling: touch;
                     height: calc(100vh - 150px);
                     overflow: auto;
                 }