Looks like you may have just taken the size provided as the max size and gone down from there. If that's the case, and you would prefer UA defaults:

```
.cm-header1 { font-size: 2em; }
.cm-header2 { font-size: 1.5em; }
.cm-header3 { font-size: 1.17em; }
.cm-header4 { font-size: 1em; }
.cm-header5 { font-size: .83em; }
.cm-header6 { font-size: .75em; }
```

(Doesn't matter to me either way, just figured I'd provide if you wanted.)