Centering image

The problem stems from broken CSS, look for this starting point in your CSS:

 @media (min-width: 769px) {
        .inside-right-sidebar, .inside-left-sidebar {
            position: -webkit-sticky;
            position: sticky;
            top:20px
        }

        div#buddypress.buddypress-wrap {
            padding:0 40px 0 40px
        }

        div.wpforms-container-full .wpforms-form .wpforms-submit-container {
            text-align:center !important
        }

        .wpforms-confirmation-container-full, div[submit-success] > .wpforms-confirmation-container-full:not(.wpforms-redirection-message) {
            background-color: #ffffff !important;
            color:#333333 !important
        }

        @media (min-width: 769px) {
            .menu-item-has-children ul .dropdown-menu-toggle {
                display:none !important
            }
        }

        .forminator-save-draft-link {
            color:#1E73BE !important
        }

        .forminator-draft-notice.draft-success {
            background:#F0F1F1 !important
        }

        .forminator-draft-wrap .forminator-draft-notice.draft-success {
            -webkit-box-shadow:inset 2px 0 0 0 #1f72be !important
        }

        div#nsl-custom-login-form-1 div.nsl-container-inline .nsl-container-buttons {
            max-width: 260px;
            margin:0 auto
        }

        .custom-html-widget {
            text-align:center
        }

        aside.widget_media_image {
            display: flex;
            justify-content: center
        }

On that very first line the @media (min-width: 769px) { opens.
But it never gets closed ie. its missing the closing }. So everything below that line falls into that @media query that only applies screens over 769px.

So you need add in the closing bracket where its necessary.