Is the color of the container different than the sign?
No, both the container and the sign are black.
    src        edge_attr  dst
0     2   to the left of    3
1     2   to the left of   10
2     3  to the right of    2
3     4   to the left of    5
4     4   to the left of   11
5     4   to the left of    7
6     5   to the left of    7
7     5  to the right of    4
8     5   to the left of   11
9     7  to the right of    4
10    7  to the right of    5
11    8  to the right of    9
12    9   to the left of    8
13   10  to the right of    2
14   11  to the right of    4
15   11  to the right of    5