Bottom of code window hidden

On Chrome and Safari (at least) the last few lines of the left hand code window are not visible. I have to add blank lines to the end in order to be able to scroll down sufficiently.

eg, if you put the following into the code window, i only see up to line 47 (results may vary based on screen size)

```
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
```

Reproduce the issue in Chrome and Safari using the 50-line example from the report, then inspect the code-window scrolling and layout entry points. Done means the last lines can be reached without adding blank lines, across the reported browsers.

Written by the indexing model from the issue text.