www.wysiwygwebbuilder.com

How to create a breakpoint based on a different breakpoint than the default ?
By default, I have a desktop version and I make each breakpoint from 320 to 780 px. And every time I have to create flexgrid in a new way because the page is created based on default. So I need to create new breakpoint based on 320 px.

Are you saying that 320 is your default? Note the default view should always be the largest view first then go down. So you should really start with for example your Desktop->Tablets->Cell /Mobile
See the FAQ:
https://www.wysiwygwebbuilder.com/forum ... 10&t=63817

I do exactly the same.
I mean that Flex Grid needs to rebuild its cells in each breakpoint. I start from 1920 and going down. In 1920 FlexGrid is different than in 320 px. So I need draw FlexGrid again in small breakpoints. Because when I create new breakpoint, it's based on 1920 px. It's so inconvenient.

A breakpoint is always based on the default view. Because a breakpoint is basically a snapshot of the differences relative to the default view. So, only the differences compared to the default view are 'recorded'.
But in a flex grid you can use templates to quickly share layouts between breakpoints.

Please explain how to use those templates

1. In the default view, store the layout by clicking the 'Add' button
2. Then in the breakpoint select the newly added template from the list.

It's very usefull! Thanx!

does a large number of breakpoints slow down the page?

If you reuse most objects, then it will not have a huge impact on the page speed.