fix(Swal): add style

Author: ArgoZhang

src/BootstrapBlazor/Components/SweetAlert/SweetAlert.razor.scss

@@ -1,3 +1,8 @@
+.swal {
+    --bb-swal-zindex: 1075;
+    z-index: var(--bb-swal-zindex);
+}
+
 .swal2-header {
     display: flex;
     flex-direction: column;