Multiple UI Improvements (#4069)

Minor contast fix for file uploading text.

Updating icon markup

Fixing icon for mentions

Removing irrelevant characters

Updating closing tag for mentions icon

webapp/sass/responsive/_mobile.scss

@@ -5,6 +5,8 @@
         .tutorial__content {
             .tutorial__steps {
                 margin-bottom: 0;
+                min-height: auto;
+                padding-bottom: 8em;
             }
         }
     }