Tips and tricks

Go to your editor. Add 3 columns for example

Let’s say we want the first and last column at 10% width

Write for the COLUMN element the Additional CSS Class of first-last-10perc

Go to Dashboard > Customize > Extra css and enter

.first-last-10perc >.wp-block-column:first-child{
	flex-basis: calc(10% - 16px);
}
.first-last-10perc >.wp-block-column:last-child{
	flex-basis: calc(10% - 16px);
}