#register_form input[type="submit"] {
    background: url("https://up-kapihospital-pics.wavecdn.net/v2/landing/form/btn_fr.webp") no-repeat;
}
#register_form input[type="submit"]:hover {
    background: url("https://up-kapihospital-pics.wavecdn.net/v2/landing/form/btn_hover_fr.webp") no-repeat;
}