XAML: how to style TextBox and PasswordBox?

Question

WPF

So.
Given:
WPF project.
There are fields:
1) Login (textbox)
2) Password (passwordbox)
3) Captcha (
textbox
) black color.
And also, so that this underline becomes gray #333 (grey) when focused, and not the notorious blue, as by default in WPF ...
How to implement?