Update _mixins.scss

assets/sass/config/_mixins.scss

@@ -58,3 +58,26 @@
         clear: both;
     }
 }
+
+
+
+/**
+ * Positioning
+ */
+
+@mixin center($horizontal: true, $vertical: true) {
+    position: absolute;
+    @if ($horizontal and $vertical) {
+        top: 50%;
+        left: 50%;
+        transform: translate(-50%, -50%);
+    } 
+    @else if ($horizontal) {
+        left: 50%;
+        transform: translate(-50%, 0);
+    } 
+    @else if ($vertical) {
+        top: 50%;
+        transform: translate(0, -50%);
+    }
+}