Hi @javadxth,
We found you have solved the problem by adding the custom css code of making fixed width of 991px to the selector ‘navbar-brand‘.
It’s good but making a fixed width of 991px will affect on smaller screen devices. so for better solution to make the site title and tagline section width to 100%, Please remove the width you added to navbar-brand and paste the below custom CSS code in Appearance > Customize > Additional CSS.
.navbar-head .col-lg-4 {
-ms-flex: 0 0 100%;
flex: 0 0 100%;
max-width: 100%;
}
Thanks