#tree svg {
    display: block;
    width: 100%;
    height: auto;
}
#tree a:hover circle,
#tree circle.selected {
    stroke: #808080;
    stroke-width: 2;
}
/* titles never intercept the mouse, so nodes under them can be hovered and clicked */
#tree text {
    pointer-events: none;
}
#tree circle {
    cursor: grab;
}