Modifying tagline display

Try adding this to your child theme style.css file:

#site-description {
    text-align: center;
    width: 400px;
}

that worked!thanks for the quick response.
is it advisable to add properties such as “font” and “color”, “font weight” to the above code in the style.css file to modify those features?

Sure thing — since you have a child theme, you can modify the CSS all you want — just put the changes in the child theme CSS file (not the parent one).

I would go with max-width property so that you can see tagline also in mobile phones.

#site-description {
    text-align: center;
    max-width: 400px;
}