SELECT element errored state

[DavidChristiansen]

I believe the select's errored state should be #{$pl_prefix}select--error

[jsutcliffe]

Hi -- is the rationale for this that you find it strange that we use the ds_input--error class for select elements? I'm not convinced that duplicating that style to a different class is the answer, just because of having to make sure they stay in sync. A couple of alternatives that might work:

• Use something more generic, e.g. ds_field--error (I know that doesn't exactly fit with the BEM we're mostly trying to use here as it's not modifying a ds_field definition)
• Pop the error styles into a mixin that is used for both input and select