Editing copyright footer code

Hello, hired a developer to edit the copyright footer. He told me to try to add this to footer css, but since I use child theme, is not an option. How can I implement this code in a child theme, maybe on style or functions? I tried on additional css but changes did not happen.

body {
    margin: 0;
}
.lenos-footer {
    background-color: #333;
    color: #eee;
    text-align: center;
}
.footer-container {
    max-width: 1190px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 15px 50px;
}
.footer-container .copyright {
    font-size: 17px;
}
.ssl-secure-payment {
    display: flex;
    align-items: center;
}
.ssl-secure-payment-left {
    display: flex;
    align-items: center;
}
.ssl-secure-payment-header {
    font-size: 17px;
    font-weight: bold;
    margin: 0;
    margin-bottom: 15px;
}
.ssl-secure-payment-des {
    font-size: 16px;
    margin: 0;
}
.ssl-secure-payment-wrapper {
    text-align: start;
}
@media (max-width: 1200px) {
    .footer-container {
        flex-direction: column-reverse;
    }
    .ssl-secure-payment {
        margin-bottom: 10px;
    }
}
@media (max-width: 900px) {
    .ssl-secure-payment {
        flex-direction: column;
    }
    .ssl-secure-payment-left {
        margin-bottom: 10px;
    }
}

By coptight footer, I mean the one at the very end. Which does not have any built-in theme editing options other than adding a text line in the theme options. https://ibb.co/1TqGpSh