Cannot automated sign in for dropbox.com through Selenium (Java) - selenium

Question

Hello I am new to automation and i have tried automating dropbox.com sign in but my code is failing after clicking on sign in link. i am not able to pass the values (username and password) in the frame of the sign in box. Following is my code.
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
public class Drop_box {
public static void main(String[] args) throws InterruptedException {
// TODO Auto-generated method stub
WebDriver driver = new FirefoxDriver();
driver.get("http://www.dropbox.com");
driver.manage().window().maximize();
driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
driver.findElement(By.xpath("//*[#id='sign-in']")).click();
driver.findElement(By.xpath("//*[#id='pyxl1851']")).sendKeys("123#gmail.com");
driver.findElement(By.xpath("//*[#id='pyxl1854']")).sendKeys("1234");
driver.findElement(By.xpath("//*[#id='regular-login-forms']/form[1]/div[3]/button")).click();
}
}

Answer 1

This should work:
driver.findElement(By.cssSelector("a#sign-in")).click();
driver.findElement(By.cssSelector("div#index-sign-in-modal input[name='login_email']")).sendKeys("email");
driver.findElement(By.cssSelector("div#index-sign-in-modal input[name='login_password']")).sendKeys("password");
driver.findElement(By.cssSelector("div#index-sign-in-modal div.sign-in-text")).click();
If you prefer xpath over css selectors, then use following lines of code:
driver.findElement(By.xpath("//*[#id='sign-in']")).click();
driver.findElement(By.xpath("//div[#id='index-sign-in-modal']//input[#name='login_email']")).sendKeys("email");
driver.findElement(By.xpath("//div[#id='index-sign-in-modal']//input[#name='login_password']")).sendKeys("password");
driver.findElement(By.xpath("//div[#id='index-sign-in-modal']//div[#class='sign-in-text']")).click();