How to edit lines above site title

You can change the colour by adding some custom CSS and modifying the hex code in this CSS:

.site-branding {
    border-bottom: 15px double #16A085;
}

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.

As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.

Okey i did it, but why other lines did not change, and search bar ?

Because in your original question you only mentioned wanting to change the lines near the site title 🙂

If you look through the theme’s stylesheet for all instances of 15px double #16A085 you’ll see which other classes need to be modified. I found three others in addition to site-branding.

So give this a try, replacing 16A085 with your colour:

.site-branding, .main-navigation:after, #social-links, .widget {
    border-bottom: 15px double #16A085;
}

Can i create pink.css and add to selection in theme ?

The recommended methods for adding custom CSS are listed above.