feat: 🎸 enable to disable border-radius (closes #38)

Author: ttskch

dist/select2-bootstrap4.css

@@ -129,9 +129,11 @@ form.was-validated select:valid ~ .select2-container--bootstrap4 .select2-select
 
 .select2-container--bootstrap4 .select2-dropdown {
   border-color: #ced4da;
-  border-top: none;
-  border-top-left-radius: 0;
-  border-top-right-radius: 0; }
+  border-radius: 0; }
+  .select2-container--bootstrap4 .select2-dropdown.select2-dropdown--below {
+    border-top: none;
+    border-bottom-right-radius: 0.25rem;
+    border-bottom-left-radius: 0.25rem; }
   .select2-container--bootstrap4 .select2-dropdown.select2-dropdown--above {
     border-top: 1px solid #ced4da;
     border-top-left-radius: 0.25rem;

dist/select2-bootstrap4.min.css

@@ -21,7 +21,7 @@
     .select2-selection__choice {
       color: $dark;
       border: 1px solid darken($light, 20%);
-      border-radius: $btn-border-radius-sm;
+      @include border-radius($input-border-radius-sm);
       padding: 0;
       padding-right: 5px;
       cursor: pointer;

src/_multiple.scss

@@ -42,7 +42,7 @@
 // search box
 .select2-search--dropdown .select2-search__field {
   border: $input-border-width solid $input-border-color;
-  border-radius: $input-border-radius;
+  @include border-radius($input-border-radius);
 }
 
 // no result message

src/_single.scss

@@ -83,16 +83,18 @@
   // dropdown
   .select2-dropdown {
     border-color: $input-border-color;
+    border-radius: 0; // overwrite select2.css
 
-    border-top: none;
-    border-top-left-radius: 0;
-    border-top-right-radius: 0;
+    // dropdown opened below
+    &.select2-dropdown--below {
+      border-top: none;
+      @include border-bottom-radius($input-border-radius);
+    }
 
     // dropdown opened above
     &.select2-dropdown--above {
       border-top: 1px solid $input-border-color;
-      border-top-left-radius: $input-border-radius;
-      border-top-right-radius: $input-border-radius;
+      @include border-top-radius($input-border-radius);
     }
 
     // selected item