If you would like to change the colors of the theme, you can use this custom sample CSS code. You can save this code in the 'Header Scripts' box on the 'Settings'-'General Settings' page.

<style>
    .navbar-bg {
        background-color: #fa0404
    }
    .btn-primary, .btn-primary.disabled {
        background-color: #fa0404;
        border-color: #fa0404;
    }
    .nav-pills .nav-item .nav-link.active {
        background-color: #fa0404;
    }
    .nav-pills .nav-item .nav-link {
        color: #fa0404;
    }
    .list-group-item.active {
        background-color: #fa0404;
    }
    .list-group-item.active {
        z-index: 2;
        color: #fff;
        background-color: #fa0404;
        border-color: #fa0404;
    }
    a {
        color: #fa0404;
    }
    .btn-primary, .btn-primary.disabled {
        background-color: #fa0404;
        border-color: #fa0404;
    }
    .btn-primary:active, .btn-primary:hover, .btn-primary.disabled:active, .btn-primary.disabled:hover {
        background-color: #fa0404 !important;
    }
    .card.card-primary {
        border-top: 2px solid #fa0404;
    }
</style>