fixed box-shadow with select2 bootstrap4 theme

build/scss/plugins/_select2.scss

@@ -191,6 +191,12 @@
   }
 }
 
+// Select2 Bootstrap4 Theme overrides
+.select2-container--bootstrap4 {
+  &.select2-container--focus .select2-selection {
+    box-shadow: none;
+  }
+}
 
 // Background colors (theme colors)
 @each $name, $color in $theme-colors {

dist/css/adminlte.css

@@ -23209,6 +23209,10 @@ html.maximized-card {
   border-top-right-radius: 0;
 }
 
+.select2-container--bootstrap4.select2-container--focus .select2-selection {
+  box-shadow: none;
+}
+
 .select2-container--default .select2-primary.select2-dropdown .select2-search__field:focus,
 .select2-container--default .select2-primary .select2-dropdown .select2-search__field:focus,
 .select2-container--default .select2-primary .select2-search--inline .select2-search__field:focus,