#1. All Blog Posts
You can follow these steps to change Blog Posts text width
First, edit a Blog Post > Click Edit Section

At Content Width > Choose Custom > Then enter your width

#2. All Blog Posts Width (Desktop Only)
Use this code to Custom CSS box
@media screen and (min-width:768px) {
.blog-item-inner-wrapper {
max-width: 600px !important;
width: 100% !important;
}
}
#3. All Blog Posts Width (Mobile Only)
Use this CSS code
@media screen and (max-width:767px) {
.blog-item-inner-wrapper {
width:95% !important;
}
}