Hi,
By default, when you click on the ok button of the contact form, the fields become red like this:
monosnap.com/file/c5S3LW0pKSwu8KZTBwgrXgB46eFSCq
This is done by adding a class "invalid" to the input fields which is normally defined in the Joomla template.
The fact that you don't see the fields color change is probably because your template doesn't define it.
In that case, you can add such CSS to your template's CSS:
.invalid {
border: 1px solid #9d261d;
background: #f2dede;
}
And yes, the buttons disappear when you click on them and are replaced by an loading image so that the customer doesn't click on them several times so that the contact request isn't sent several times if your server takes a few seconds to process the contact request.