Use transparent background for modal

src/styles/_app_base.sass

@@ -345,15 +345,14 @@ input, input.form-control
 
 
 /* Modal Bootstrap overrides */
+.modal-dialog
+	margin-top: 0
 .modal-content
 	border: none
-	border-radius: 3px
 	box-shadow: 0 0 25px rgba(black, .25)
 	background-color: $color-background-light
 
 	.modal-header
-		border-top-left-radius: 3px
-		border-top-right-radius: 3px
 		background-color: white
 		padding: 10px 10px 10px 15px
 
@@ -370,7 +369,7 @@ input, input.form-control
 				color: $color-primary
 
 .modal-backdrop
-	background-color: $color-background-nav
+	background-color: transparent
 
 .modal-help-panel
 	overflow: hidden