Contact Enhanced tries to inherit most of your template's styling, however some templates have HTML override for Joomla core components and/or style your core components differently. In these cases sometimes your custom field's borders will disappear. When this happens you will have to add the line below to the CE's CSS file:

If using Joomla 2.5 and newer, create a CSS Form Field type and add the CSS rule below:

.ce-container .inputbox{border:1px inset !important}