Responsive page with Flexbox

What are you most proud of, and what would you do differently next time?

I' so proud of my CSS and HTML code. The reasons are:

• Well-structured code.
• Order of properties's selectors in CSS.

What challenges did you encounter, and how did you overcome them?

Flexbox, I've never used flex-basis to resize the content of elements inside flexbox.

What specific areas of your project would you like help with?

I would like to get help in:

• Rem units for all the elements a good way? . I write my css code using rem units for paddings, font-sizes but html font-size, margins, etc. it is correct? or I should use other units?

Is this a good order for the properties?

1. positioning : display, position, visibility, z-index...
2. box model: box-sizing, width, height, margin, padding, border, b-radius...
3. Typography: ffamily, f-size, line-height, f-weight, f-style, text-align, t-transf., t-decora, color...
4. background and border: bg, bg-color, bg-image, border, b-color, b-shadow, etc
5. spacing and alignment: text-align, overflow, etc
6. animations and transformations
7. others