Sheet name font size on LibreOffice Calc is too small

I am using LibreOffice 3.5.3.2 (Ubuntu 12.04) and the buttons to switch tabs in Calc are written with small fonts. They're so small I can't even read what is written on them.

I could not find a way to increase font size. Is this problem happenning only with me? Does anyone know a way to increase the font size of sheet names?

I had similar problem with elementary theme. Although the problem was that the scrollbars were too thin. The fix was to modify the scrollbar width in gtkrc file, in my case:

/usr/share/themes/elementary Dark/gtk-2.0/gtkrc

find:

GtkScrollbar            ::slider-width

and set the value to something like 10

Different themes can have different effect on applications. Sometimes this can cause serious problems as shown below. Sheet tabs are hardly readable in first theme but are very clear in second theme.

So changing your system theme can solve this problem.