html.task-mail #layout-sidebar {
    flex: 0 0 220px !important;
    width: 220px !important;
    max-width: 220px !important;
    min-width: 220px !important;
}

html.task-mail.action-compose #layout-sidebar {
    flex: 0 0 260px !important;
    width: 260px !important;
    max-width: 260px !important;
}