To fix this issue
Convert <left>, <data>, <right> tags → <div class="left">, etc.
<left>, <data>, <right>
<div class="left">
Update CSS grid-template-areas to use .left, .right, .data.
.left
.right
.data
Confirm hidden form has plain display: none; with no competing styles.
display: none;
test.html
grid.css