Add flexbox helpers

Add of flexbox helpers ( display, direction, flow, wrap, align, justify-content)

Split colors helpers

Split helpers colors into individual helpers

Add fill-color helper and examples of colors helpers

Creation of the fill-color helper,
and added the examples of text-color, bg-color, border-color and fill-color

Update skin last minute text

• Update skin last minute text #483

Add new arrows pictos

• Replacement of old version of pictos arrows by the news, to update the charter

Add helper for native-foreground color

• Add helper for native-foreground color

Minor Darkmode variable improvement

• Improve base and native background/foreground color couples
• Replace the arrows symbols

Make box-edge color configurable

• Make box-edge color configurable by stylus
• Remove useless --box-color css property

Fix icon fallback color for IE

Fix CSS custom properties fallback .icon colors

Block title border-color

Fix the color for the dark mode