Lack of leading digit in front of decimal dot makes decimal dot syntax group wrong

[Aster89]

The issue is originally posted on Vim: vim/vim#11472

See the coloring of . in the following snippet with and without the 0.

.some-class {
  --some-var: 0.2s;
}

When the 0 is not there, :echo map(synstack(line('.'), col('.')), 'synIDattr(v:val, "name")') returns

• for ., ['cssDefinition', 'cssAttrRegion'],
• for 2, ['cssDefinition', 'cssAttrRegion', 'cssValueTime'],
• for s, ['cssDefinition', 'cssAttrRegion', 'cssValueTime', 'cssUnitDecorators']

whereas if th 0 is there it returns

• for 0, ['cssDefinition', 'cssAttrRegion', 'cssValueTime'],
• for ., ['cssDefinition', 'cssAttrRegion', 'cssValueTime'],
• for 2, ['cssDefinition', 'cssAttrRegion', 'cssValueTime'],
• for s, ['cssDefinition', 'cssAttrRegion', 'cssValueTime', 'cssUnitDecorators']

I expect the syntax coloring of . to be not dependent on whether there's a leading digit in front of it.