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+**Display**
+display none vs visibility hidden: display: none is really like the element does not exist. Visibility hidden just hides it but it still takes space.
+
+A display: none element can still have size and be coloured with a background image. It still doesn't take space. This can be used for a timeline bar for example!
+
+**Flexbox**
+Flexbox deals with layout always in only one dimension; it's possible to specify which dimension: either vertical or horizontal.
+
+Two axes: main and cross
+
+Control main axis: `flex-direction: row|row-reverse|column|column-reverse`. The first two make it a horizontal layout and the latter make it a vertical layout.
+
+Cross axis is always the opposite of `flex-direction`, so if `flex-direction: row-reverse` the cross axis is `column-reverse`.
+
+The writing mode determines where the start and end are, based on for example languages. Japanese is written from right-to-left rather than western left-to-right.
+So while in Europe the start of a flexbox is at the left and the end at the right in Japan this would be reversed.
+
+**Relationships**
+An important aspect of creating layouts with CSS is the relationships of elements with each other. For example parent/child relationships.
+
+If we change the width of a parent element; the height of all children increase. This happens because the total area of the parent remains the same.
+
+When the edge of a child aligns with its parent and we add a margin to the child; it pushes to the parent as well. This phenomenon is called ==collapsing margins==. It can be prevented by unaligning the edge(s) for example by adding padding or setting `display: flow-root;`.
+
+In `flexbox` siblings push against each other; if we add padding to one, it pushes against the other making it smaller. This does not happen in grid, where each cell gets a fixed size and the padding pushes against its own side.
+
+**Centering stuff**
+Use `margin-inline: auto;` -> this adds margins on both sides of the element. This can be used to center stuff on the page for example.
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