Someone on Sustainable Living SE proposed to hold a 'new logo' contest so we can make the beta site a bit more distinct and recognizable. From this Meta post I understood that Stack Exchange sites can propose a new logo, although that post doesn't say if this only applies to mature sites or also beta sites. In any case I'd like to know what exactly the requirements are for a site logo? Are there specific dimensions for example? Minimum of padding?
From a look at the list of all SE sites I noticed that all logo's there are 48x48 pixels (favicon.ico is 32x32). Also most logos have several pixels padding, although the exact amount seems to vary. Furthermore I see that the dimensions of a logo on a site itself varies; the logo on Biology SE is 139 x 50 pixels, Network Engineering has 218 x 51 and World Building has 238 x 37 pixels for example. Is it correct to say that logo dimensions should be roughly 240 x 51 as a maximum?