displays child blocks in a responsive FLEXBOX grid

syntax 1 : {up flexbox=x1-x2}content with several child blocks{/up flexbox}
syntax 2 : {up flexbox=x1-x2}content block-1 {======} content block-2{/up flexbox}
x1-x2 are the relative widths of the columns
example : col=4-8 or col=33-66 for 2 columns (equivalent: span4 and span8)

🟩 upbtn-makefile PREFS.INI :
options (default) : class=fg-gap
2-10 : flexbox=2-10 | tablet=3-9 | mobile=4-8 | class=fg-gap | bloc-style=padding:0 10px
4-8 : flexbox=4-8 | tablet=2-10 | mobile=1 | class=fg-gap | bloc-style=padding:0 10px
3-6-3 : flexbox=3-6-3 | tablet=4-4-4 | mobile=1 | class=fg-vspace-between-1 m-child-raz-1 fg-gap | bloc-style=padding:0 10px
4-8-gris : flexbox=4-8 | tablet=2-10 | mobile=12 | class=fg-gap | bloc-style=padding:10px 10px 0;border:1px solid #999
8-4-gris : flexbox=8-4 | tablet=8-4 | mobile=12 | class=fg-gap | bloc-style=padding:10px 10px 0;border:1px solid #999