Pick direction, wrap, justify, align and gap, then copy the flex CSS with a table of what each value does.
The page writes one container rule. With the defaults it is display: flex; flex-direction: row; flex-wrap: nowrap; justify-content: space-between; align-items: center; gap: 16px;. The gap line is left out when the gap is 0, and align-content is left out while it is set to normal, its default. A second block is an optional item rule, flex: 1 1 200px, which means grow, shrink and start from 200 px. The third block is HTML for 1 to 12 items so you can paste a working example. Gap accepts 0 to 200 px. Nothing is stored or uploaded; the CSS is worked out in your browser.
Flexbox works along two axes. The main axis follows flex-direction: row runs along the inline direction, from start to end, row-reverse from end to start, column along the block direction and column-reverse against it. In left-to-right horizontal text, inline is left to right and block is top to bottom, so row runs left to right and column top to bottom; a right-to-left language or a vertical writing mode changes that. The cross axis is the other one. justify-content places items along the main axis, and align-items places them along the cross axis. That is why centering needs both: justify-content: center and align-items: center put a single item in the middle of its box. When you switch the direction from row to column, the same two properties swap which way they act, and the table under the CSS rewrites its sentences to match the direction you chose.
By default (nowrap) all items stay on one line and shrink to fit. With wrap, items that do not fit start a new line, and the lines can then be positioned as a group with align-content. That property does nothing on a single line, which is why the table says so. With three items of 300 px in a 700 px container, wrap puts two on the first line and one on the second, while nowrap squeezes all three into one line. wrap-reverse stacks the lines in the opposite cross direction.
The gap property puts space between flex items only. It adds nothing before the first item or after the last, so you do not have to remove a margin from the end items. With 4 items and gap: 16px, the container holds 3 gaps of 16 px, which is 48 px, and the items share the rest. When items wrap onto a second line, the same gap also separates the lines. Type 0 to remove the gap line from the CSS. If you want space at the outer edges too, add padding to the container; this page does not write padding.
The page has no picture of the layout, because its preview box cannot show a flex layout, so the table of values is the explanation. It writes only the container, plus one example item rule. It does not write order, align-self, flex-flow, margin tricks or per-item grow and shrink values. Reverse directions (row-reverse, column-reverse, wrap-reverse) change what you see but not the keyboard or screen reader order, which still follows the HTML; the page adds a note when you choose one.
Give the parent display: flex; justify-content: center; align-items: center; and a height, such as 300px. The first centers the child along the main axis and the second along the cross axis. Choose center in both justify-content and align-items here and copy the CSS.
justify-content works along the main axis, set by flex-direction, and align-items works across it. In a row, justify-content is horizontal and align-items is vertical. In a column the two swap: justify-content becomes vertical.
It only positions lines of items, so it needs flex-wrap: wrap and enough items to fill more than one line. On a single line, as with nowrap, there is just one line to place and align-items does the work. The table under the CSS says this for the value you chose.
With 3 items in 600 px and 120 px of free space, space-between puts 60 px between items and none at the ends, space-around gives each item 20 px on each side (20 px at the ends, 40 px between), and space-evenly gives 30 px in all four places.
Use gap, for example gap: 16px;. It adds 16 px between items in both directions and none outside them, so you do not need margins on the items. Type a number in the gap box and the CSS updates.
No. The CSS is worked out in your browser and nothing is uploaded or stored. Page visits are counted with Google Analytics, never your choices.