Fixed table head - CSS-only

關鍵在使用position: sticky;來釘住table header。
參考：CSS-Only Scrollable Table with fixed headers

head1	head2	head3	head4
row 1, cell 1	row 1, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 1, cell 1	row 1, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 1, cell 1	row 1, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 1, cell 1	row 1, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2
row 2, cell 1	row 2, cell 2	row 1, cell 2	row 1, cell 2