Please clarify your request with more details. I see that tagline is already added into the style.css. You may also create custom.css to prevent overwriting your changes during theme update. Please watch here how to create custom.css: https://www.youtube.com/watch?v=Qok2zRedRMY
You can write blog description in Theme Options > General > Header Settings > Header custom HTML for some variantsFor variants 1, 2, 8, 10. But it can be shown only for some header types – 1, 2, 8, 10.