Top bar logo causes page jump during load

[mvl22]

The header/logo at the top of the page appears quite late in the loading cycle, especially on mobile, e.g.:

https://raven.cam.ac.uk/

As a result, I've often found that, when using Raven, I move my finger to the username field, but the page then jumps down, requiring a second click to the new location.

Is it possible at least to give the top logo a height? Currently the code is:

<img alt=""  src="/images/interface/main-logo-small.png" />

Or is the problem slow loading of the whole header? (I can't immediately tell.)

[tombsar]

This should be fixed by 796f39b.