It was just few week back I asked for Flexible Box Layout Module in the Feature request / Suggestion forum and now I feel my dream comes true and it's surely one of most value-able feature beside many other new features of RSD and I am really grateful for such significant development.

Beside all great new feature I totally love Height % for Column and Rows as well.

Looking forward viewport units support (vw, vh, vmin, vmax ) as well and hopefully very soon

I hope you also that these institutions come

Hello Mansour, I'm hoping that you or maybe Eric Rohloff do some videos on flex box. Im trying to realize the power and usefulness of flexbox. I find it difficult to follow fast paced tutorials with no spoken dialogue and music only.
Thanks in advance if you decide to do a few videos of your RSD flexbox findings.
-WMFX

No worries I will try my best once we have the final version.
for now I advice you watch this.
https://www.youtube.com/watch?v=G7EIAgfkhmg

In the Position section of the Design panel, the ability to change a container's Display property to Flex created for me a completely new area of RSD learning fun.

I'm finding the Flexbox Playground at https://scotch.io/demos/visual-guide-to-css3-flexbox-flexbox-playground (Note) pretty useful, though I have to have my browser window filling the screen, and I have to adjust the page size in that window (using Ctrl-minus) to see it in full.

Frank

Note: part of https://scotch.io/tutorials/a-visual-guide-to-css3-flexbox-properties.

Great video find Mansour thanks!