Got some problem with the rectangle it ain't displaying

Answer 1

_use this code inside <header> tag:
<svg width="put a number" height="put a number">
<rect width="put a number" height="put a number" fill="put a color name">
</rect>
</svg>
_to make the rectangle animated put this code after rect tag:
<animate attributename="x" from="put a number" to="put a number" dur="xs"fill="freeze" repeatcount="put a number"/>

Answer 2

instead of x in "dur" also put a number for example 3s