If it helps the css I ended up going with below. Note I am in learn / try things out mode atm so not saying this css will stand up thru the whole application. Also select boxes remain grey - I am OK with that as they have darker placeholder text and seem to look OK. Anyway CSS is:
.input-with-feedback:not([data-fieldtype=Check]).form-control:not([data-fieldtype=Check]),
.form-control:not([data-fieldtype=Check])
{
background-color: white;
border: solid 1px dimgray;
}
.input-with-feedback:not([data-fieldtype=Check]):focus {
background-color: white;
box-shadow: 0 0 0 2px hsl(198.6 88.7% 48.4% / 40%);
}
Gives an appearence like:
Note: the hsl color is the one shoelace.style uses
