Hi,
There is no CSS styles missing. The problem is from your template's CSS styles.
To make the amount radio button shown one per line, you can override your template's CSS by adding
.cmgiftcard #jform_defined_amount label {
display: block;
padding-left: 5px;
}
to the bottom of components/com_cmgiftcard/assets/css/style.css or to your template's custom CSS file if your template has this file.
Regards,
Hung Tran