Are there white letters or numbers?
No, there are numbers but they are black.
    src        edge_attr  dst
0     0   to the left of    5
1     0   to the left of    4
2     1   to the left of    4
3     1   to the left of    5
4     1   to the left of   10
5     2   to the left of   10
6     2   to the left of    9
7     3               on    1
8     3   to the left of    8
9     4  to the right of    0
10    4  to the right of    8
11    4  to the right of    7
12    4   to the left of    9
13    4   to the left of   10
14    4  to the right of    1
15    4  to the right of   11
16    5  to the right of    0
17    5  to the right of    8
18    5  to the right of   11
19    5  to the right of    1
20    7   to the left of    4
21    8   to the left of    5
22    8  to the right of    3
23    8   to the left of    4
24    9  to the right of    4
25    9  to the right of    2
26   10  to the right of    1
27   10  to the right of    4
28   10  to the right of    2
29   11   to the left of    4
30   11   to the left of    5