Fix #903 litepicker with date range not having correct border (#980)

src/scss/vendor/_litepicker.scss

@@ -17,11 +17,13 @@
     fill: none !important;
   }
 
-  .container__months {
+  .container__main {
     border: 1px solid var(--#{$variable-prefix}border-color);
     border-radius: $border-radius;
     box-shadow: $dropdown-box-shadow;
+  }
 
+  .container__months {
     .month-item-name,
     .month-item-year {
       font-weight: $font-weight-medium !important;