You are facing a complex background propagation that you can read about here. I will try to explain it with simple words.
Your body
has a height equal to 0; thus the background won't be visible on it but by default it has 8px
of margin which create a height of 8px
on the html
element.
Why not 16px of height (8px for top + 8px for bottom)?
Since the height of body is 0 we are facing a margin collpasing and both margin will collapse into only one and we have a height of 8px.
Then we have a background propagation from body
to html
and the linear-gradient
will cover the 8px height.
Finally, the background of the html is propagated to the canvas element in order to cover the whole area which explain why the linear gradient is repeating each 8px
.
body {
background: linear-gradient(to top, red, yellow);
}
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