IWebElement clickUsername = driver.FindElement(By.XPath("//input[@name='tbUsername']"));
        clickUsername.Click();
        clickUsername.SendKeys("MyUsername");


        IWebElement clickPassword = driver.FindElement(By.XPath("//input[@name='tbPassword']"));
        clickPassword.Click();
        clickPassword.SendKeys("Mypassword");

<div class="inputbg">
    THIS IS VISIBLE => <input id="dummypassword" class="input" type="text" onfocus="this.style.display='none';document.getElementById('pw').style.display='inline';document.getElementById('pw').focus()" value="Password" tabindex="2" name="dummypassword">
    THIS IS INVISIBLE => <input id="pw" class="input" type="password" onblur="if(this.value==''){this.style.display='none';document.getElementById('dummypassword').style.display='inline'}" onkeypress="if (event.keyCode==13)fmLogin.submit();" value="" style="display: none;" tabindex="2" name="tbPassword" autocomplete="off">
</div>

IWebElement clickPassword = driver.FindElement(By.Id("dummypassword"));
clickPassword.Click();

IWebElement realPasswordInput = driver.FindElement(By.XPath("//input[@name='tbPassword']"));
realPasswordInput.SendKeys("Mypassword");

allTextBoxes = driver.FindElements(By.Id("username"));
        var allPasswordTextBoxes = driver.FindElements(By.Id("password"));

        var userNameTextField = allTextBoxes.Count > 0 ? allTextBoxes[1] : allTextBoxes[0];
        userNameTextField.SendKeys("myUsername");

        var passwordTextField = allPasswordTextBoxes.Count > 0 ? allPasswordTextBoxes[1] : allPasswordTextBoxes[0];
        passwordTextField.SendKeys("myPassword");