gap property for Flexbox

`gap` for flexbox containers to create gaps/gutters between flex items

CSS3 Multiple column layout

Method of flowing information in multiple columns

css property: -webkit-column-axis

css property: -webkit-column-break-after

css property: -webkit-column-break-before

css property: -webkit-column-break-inside

css property: -webkit-column-progression

css property: column-count

css property: column-count: auto

css property: column-fill

css property: column-fill: auto

css property: column-fill: balance

css property: column-fill: balance-all

css property: column-gap

css property: column-gap: supported in flex layout

css property: column-gap: supported in grid layout

css property: column-gap: supported in multi-column layout

css property: column-gap: supported in multi-column layout: `calc()` values

css property: column-gap: supported in multi-column layout: `<percentage>` values

css property: column-rule

css property: column-rule-color

css property: column-rule-style

css property: column-rule-width

css property: column-span

css property: column-span: all

css property: column-span: none

css property: column-width

css property: column-width: auto

css property: display: table-column-group

css property: flex-direction: column-reverse

css property: grid-column-end

css property: grid-column-start