Hi there,
you can use some CSS like this:
@media(min-width: 769px) {
.grid-container {
max-width: 80% !important;
}
.site.grid-container,
.gb-container.width-80>.gb-inside-container {
max-width: calc(80% - 80px) !important;
}
}
Note this CSS selector: .gb-container.width-80>.gb-inside-container
This will apply to any GenerateBlocks Container Blocks that you want the 80% width applied to by:
1. Select the Container Block
2. In Advanced > Additional CSS Class(es) add: width-80