HTMLテンプレートやBootstrapを追加

app/assets/scss/material-dashboard/_alert.scss

@@ -0,0 +1,17 @@
+@each $state, $value in $theme-gradient-colors {
+  .alert-#{$state} {
+    @include gradient-directional(nth($value, 1) 0%, nth($value, -1) 100%, $deg: 195deg);
+  }
+}
+
+.btn-close {
+  &:focus {
+    box-shadow: none;
+  }
+}
+
+.alert-dismissible {
+  .btn-close {
+    background-image: none;
+  }
+}