I’ve added an inner table for the year/car model tabular content. This table is using css fixed layout, so that I can remove all width definitions from all columns except “Type”. The remaining columns have identical widths.
|-
|
{| style="width:100%; table-layout:fixed; margin:0" class="wikitable"
|- bgcolor=#F0F0F0
|rowspan= 2 style="width:8em"| '''Type'''
|colspan=10| 1970s
|colspan=10| 1980s
|colspan=10| 1990s
|colspan=10| 2000s
|- bgcolor=#F0F0F0
|0||1||2||3||4||5||6||7||8||9
|0||1||2||3||4||5||6||7||8||9
|0||1||2||3||4||5||6||7||8||9
|0||1||2||3||4||5||6||7||8||9
Maybe better colors? More contrast, anyway, and way simpler code:
Yet another option, with borders separated and cellspacing=0 for wider borders between table cells: