Implement dark theme (#49)

bookmarks/styles/dark.scss

@@ -0,0 +1,27 @@
+/* Dark theme overrides */
+
+/* Buttons */
+.btn.btn-primary {
+  background: $dt-primary-button-color;
+  border-color: darken($dt-primary-button-color, 5%);
+
+  &:hover, &:active, &:focus {
+    background: darken($dt-primary-button-color, 5%);
+    border-color: darken($dt-primary-button-color, 10%);
+  }
+}
+
+/* Focus ring*/
+a:focus, .btn:focus {
+  box-shadow: 0 0 0 .1rem rgba($primary-color, .5);
+}
+
+/* Forms */
+.has-error .form-input, .form-input.is-error, .has-error .form-select, .form-select.is-error {
+  background: darken($error-color, 40%);
+}
+
+/* Pagination */
+.pagination .page-item.active a {
+  background: $dt-primary-button-color;
+}