One Page

Use code to Individual Page Header Code Injection (or Code Block if you use a Personal Plan)

<style>
footer.sections:before {
    content: "";
    display: block;
    background-color: #f1f;
    height: 2px;
    width: 100%;
    margin: 0 auto;
}
</style>

All Pages

Use code to Custom CSS box

footer.sections:before {
    content: "";
    display: block;
    background-color: #f1f;
    height: 2px;
    width: 100%;
    margin: 0 auto;
}