Template:TOC/styles.css

/* hide all links under level 2 header */
.toclimit-2 .toclevel-1 ul,
/* hide all links under level 3 header */
.toclimit-3 .toclevel-2 ul,
/* hide all links under level 4 header */
.toclimit-4 .toclevel-3 ul,
/* hide all links under level 5 header */
.toclimit-5 .toclevel-4 ul {
    display: none;
}