Aggiornamento.
Ho risolto inserendo questo codice:
.sourcecoast .btn-primary:hover, .sourcecoast .btn-primary:focus, .sourcecoast .btn-primary:active, .sourcecoast .btn-primary.active, .sourcecoast .btn-primary.disabled, .sourcecoast .btn-primary[disabled] {
background-color: #3399cc;
}
.sourcecoast .btn-primary {
background-image: linear-gradient(to bottom, #3399cc, #3399cc);
}
letto in un post del forum di sourcecoast.
Grazie a tutti.