Source Code in CVS Rule is neither using monospace nor using "pre" white-space rule
A brief look at https://osdn.jp/cvs/view/mplus-fonts/mplus_outline_fonts/Makefile?revision=1.30&view=markup illustrates the issue: all the indents are lost due to the non-pre white-space: rule, and the fonts are not set to be monospace.
Fixing this is rather trivial:
.vc_file_line_number, /* I sometimes prefer monospace for line numbers too */
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We update ViewVC CSS and add your prefered setting.