Flexbox shall not exist. At least in the way it is defined.

1. It breaks CSS box model that postulates that "width" defines element width. With flexbox that is not so as width can be overridden by flexbox in non-trivial manner.

2. flexibility shall be defined by flex/fraction units like in Grid module. So we may have:

    width: 10fr;
    margin-left: 2fr;
    border-spacing: 1fr;

3. CSS and HTML shall have unified flex units. Flexibility in HTML uses ** units like

    <frameset rows="200,1*,200"> 
    <frameset rows="200,2*,1*"> 
    <td width="2*"> 

and so CSS might use that as

    width: 10*;
    margin-left: 2*;

4. Flexibility as an entity shall be expressed uniformly among different CSS modules. Instead of bunch of separate flex-** properties and separate FR units it should be just flex units width:2*; and flex functions if that is needed.

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"box-sizing" shall have also padding-box value.

When defined padding shall go into scrollable content : https://terrainformatica.com/2019/10/17/css-overflow-padding...

In general box-sizing is broken (or under specified) in regard of paddings of the element.

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"outline" shortcut property shall include outline-offset value too.

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"visibility" shall have "none" value.

   visibility:none; 

shall be treated as display:none and display shall not have none value. So for hiding/showing a table for example we can use

   .some { 
     visibility:none; 
     visibility:visible; 
   }

But not

   .some { 
     display:none; 
     display:block; 
   }

which is obviously wrong.

In short: visibility and display model shall be orthogonal.

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Syntax:

Modules shall use functional notation rather introducing bunch of conflicting prefixed properties, so use this

   display: grid(
      column: 2 / 4,
      row: 1 / 3 
   ); 

instead of

    grid-column: 2 / 4;
    grid-row: 1 / 3;

Different modules in future may also want to have grid-columns, etc.

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