HI!

pls. use following css, for example:

.wpb-js-composer .vc_tta-color-white.vc_tta-style-classic .vc_tta-tab.vc_active>a {
     color: #000 !important;
}
.wpb-js-composer .vc_tta.vc_tta-tabs .vc_tta-tab.vc_active > a, 
.wpb-js-composer .vc_tta.vc_tta-tabs.vc_tta-style-outline .vc_tta-tab a, 
.wpb-js-composer .vc_tta.vc_tta-tabs.vc_tta-style-modern .vc_tta-tab a {
    font-family: 'Montserrat' !important;
    font-weight: bold !important;
}