The selectbox mystery of WordPress

The other day I wanted to use a selectbox with 5 elements in my plugin’s option page. No problem I thought:

What everybody including me expects is something like this:

But I actually got this:

The mystery lies in the style sheet for the admin area:

#wpcontent select {
	padding: 2px;
	height: 2em;
	font-size: 12px;

This forces every selectbox to display only one element. I have no idea why this is implemented. There is also a ticket in the WP tracking system discussing this behaviour since two years.

The solution to this problem is quite easy: