Use this custom CSS in your custom.css file
body .sppb-btn.sppb-btn-secondary:hover, body .sppb-btn.sppb-btn-secondary:focus, body .sppb-btn.sppb-btn-secondary:active, body .sppb-btn.btn-seconday:hover, body .sppb-btn.btn-seconday:focus, body .sppb-btn.btn-seconday:active, body .sppb-btn.btn-primary:hover, body .sppb-btn.btn-primary:focus, body .sppb-btn.btn-primary:active, body .btn.sppb-btn-secondary:hover, body .btn.sppb-btn-secondary:focus, body .btn.sppb-btn-secondary:active, body .btn.btn-seconday:hover, body .btn.btn-seconday:focus, body .btn.btn-seconday:active, body .btn.btn-primary:hover, body .btn.btn-primary:focus, body .btn.btn-primary:active{
background: linear-gradient(251.87deg,rgba(255,255,255,0.2) -15.74%,rgba(255,255,255,0) 58.65%),#0fe3d8 !important;
}