If you have to keep the position fixed for some reason you can give the menu a fixed height and add that value as a top margin to the paragraph.
#menu{
...
max-height: 100px;
}
p{
margin-top: 100px;
}
If you don't need position: fixed (because technically you don't if you just want to keep your header up top) you can use position: sticky
as s.kuznetsov mentioned in comments or you can just take out position, right, left, and top properties. The header will stay at the top and the paragraph will show.
#menu{
padding:30px;
background:#000;
border:5px solid #000000;
border-radius:0px;
z-index:1;
text-align:center;
}
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