You can add something to the login form of the panel:
body.login form.form {
padding-top: 150px;
background: #fff url('../images/logo.svg') center top no-repeat;
background-size: 25% auto;
}
body.login form.form::after {
color: #999;
content: 'Powered by The company';
}
body.login form.form .btn-submit {
margin: 0 0 45px 0;
}
body.login form.form fieldset.buttons-centered {
border-bottom: 1px solid #ccc;
margin-bottom: 10px;
}
Good luck!