initial implementation of bootstrap v5, purgecss, postcss, autoprefixer

assets/css/app.scss

@@ -1,5 +1,5 @@
-/* This file is for your main application css. */
-@import "./phoenix.css";
+/* Bootstrap v5 */
+@import "~bootstrap/scss/bootstrap";
 
 /* LiveView specific classes for your customizations */
 .phx-no-feedback.invalid-feedback,
@@ -55,30 +55,6 @@
 }
 
 /* Alerts and form errors */
-.alert {
-  padding: 15px;
-  margin-bottom: 20px;
-  border: 1px solid transparent;
-  border-radius: 4px;
-}
-.alert-info {
-  color: #31708f;
-  background-color: #d9edf7;
-  border-color: #bce8f1;
-}
-.alert-warning {
-  color: #8a6d3b;
-  background-color: #fcf8e3;
-  border-color: #faebcc;
-}
-.alert-danger {
-  color: #a94442;
-  background-color: #f2dede;
-  border-color: #ebccd1;
-}
-.alert p {
-  margin-bottom: 0;
-}
 .alert:empty {
   display: none;
 }