[TASK] Make sure browser validation works with custom checkboxes

src/extensions/site_t3demo/Resources/Private/Scss/_form.scss

@@ -46,6 +46,7 @@
 
 	&__field {
 		margin-top: 5px;
+		position: relative;
 	}
 
 	&__button {
@@ -134,10 +135,19 @@
 		}
 	}
 
-	/* checkbox and radios */
+	/* checkbox and radios
+	   we hide the form controls but do not remove the field with display:none; as this
+	   breaks browser native validation for required checkbox inputs
+    */
 	&__checkbox,
 	&__radio {
-		display: none;
+		display: block;
+		height: 34px;
+		width: 34px;
+		position: absolute;
+		left: -4px;
+		top: -8px;
+		opacity: 0;
 	}
 
 	&__label--checkbox,