.mdl-portalmenu__list {
    display: block;
    flex: 1;
    overflow-x: hidden;
    overflow-y: auto;
    min-width: 124px;
    margin: 0;
    padding: 0;
    list-style: none;
    box-sizing: border-box;
}
.mdl-portalmenu__list *, .mdl-portalmenu__list *:before, .mdl-portalmenu__list *:after {
    box-sizing: inherit;
}