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  • Ryan Garrett thinks this is interesting:

.field-validation-error    {color: #f00;}
.field-validation-valid    { display: none;}
.input-validation-error    { border: 1px solid #f00; background-color: #fee; }
.validation-summary-errors { font-weight: bold; color: #f00;}
.validation-summary-valid  { display: none;}

From

Cover of Pro ASP.NET MVC 5, Fifth Edition

Note

CSS specifiers used by Html.Textbox