odoo/addons/web_gantt/static/src/css/gantt.css

.openerp .oe_gantt {
    min-height: 500px;
}

.openerp .oe_gantt .oe_gantt_button_create {
    position: absolute;
    top: 5px;
}
@media print {
    .oe_gantt button {
        display: none;
    }
    .oe_gantt > table > tbody > tr > td > div > div {
        overflow: hidden !important;
    }
}