How to change the textbox color with repect to error message

Question

I want to change the error message border color on text box 

here is the code:

function ValidateFrom() {

if (document.getElementById("<%=txtCategoryName.ClientID %>").value.trim() == "") {

document.getElementById("<%=dvMessage.ClientID %>").innerHTML = "Please enter Category.";

document.getElementById("<%=txtCategoryName.ClientID %>").focus();

// document.getElmentById(val.controltovalidate).style.border = '3px solid red';

return false;

}

 by default in form-control it will takes blue..i want while changes on error message show red border..