styles: Move vertical-gradient mixin into home.scss

Author: Turbo87

app/styles/_helpers.scss

@@ -1,5 +1,4 @@
 @import "normalize";
-@import "helpers";
 
 $html-bg: #3b6837;
 $main-color: #383838;

app/styles/app.scss

@@ -1,3 +1,14 @@
+@mixin vertical-gradient($start, $end) {
+    background: $end;
+    background: -moz-linear-gradient(top, $start 0%, $end 100%);
+    background: -webkit-gradient(linear, left top, left bottom,
+        color-stop(0%,$start),
+        color-stop(100%,$end));
+    background: -webkit-linear-gradient(top, $start 0%,$end 100%);
+    background: -ms-linear-gradient(top, $start 0%,$end 100%);
+    background: linear-gradient(to bottom, $start 0%,$end 100%);
+}
+
 @mixin button($start, $end) {
     $start_dark: darken($start, 5%);
     $end_dark: darken($end, 5%);