used a fixed number of decimal places in output

Some of the numbers we output are needlessly long e.g.
```
<span class="strut bottom" style="height:1.1764999999999999em;vertical-align:-0.481108em;"></span>
```
```
<span style="top:-2.6550000000000002em;">...</span>
```
Maybe we can do `.toFixed(3)` or `.toFixed(4)` when outputting values to keep the output smaller.