table {_x000D_
overflow-y: auto;_x000D_
height: 50vh; /* !!! HEIGHT MUST BE IN [ vh ] !!! */_x000D_
}_x000D_
_x000D_
thead th {_x000D_
position: sticky;_x000D_
top: 0;_x000D_
}
_x000D_
<table>_x000D_
<thead>_x000D_
<tr><th>TH 1</th><th>TH 2</th></tr>_x000D_
</thead>_x000D_
<tbody>_x000D_
<tr><td>A1</td><td>A2</td></tr>_x000D_
<tr><td>B1</td><td>B2</td></tr>_x000D_
<tr><td>C1</td><td>C2</td></tr>_x000D_
<tr><td>D1</td><td>D2</td></tr>_x000D_
<tr><td>E1</td><td>E2</td></tr>_x000D_
<tr><td>F1</td><td>F2</td></tr>_x000D_
<tr><td>G1</td><td>G2</td></tr>_x000D_
<tr><td>H1</td><td>H2</td></tr>_x000D_
<tr><td>I1</td><td>I2</td></tr>_x000D_
<tr><td>J1</td><td>J2</td></tr>_x000D_
<tr><td>K1</td><td>K2</td></tr>_x000D_
<tr><td>L1</td><td>L2</td></tr>_x000D_
<tr><td>M1</td><td>M2</td></tr>_x000D_
<tr><td>N1</td><td>N2</td></tr>_x000D_
<tr><td>O1</td><td>O2</td></tr>_x000D_
<tr><td>P1</td><td>P2</td></tr>_x000D_
<tr><td>Q1</td><td>Q2</td></tr>_x000D_
<tr><td>R1</td><td>R2</td></tr>_x000D_
<tr><td>S1</td><td>S2</td></tr>_x000D_
<tr><td>T1</td><td>T2</td></tr>_x000D_
<tr><td>U1</td><td>U2</td></tr>_x000D_
<tr><td>V1</td><td>V2</td></tr>_x000D_
<tr><td>W1</td><td>W2</td></tr>_x000D_
<tr><td>X1</td><td>X2</td></tr>_x000D_
<tr><td>Y1</td><td>Y2</td></tr>_x000D_
<tr><td>Z1</td><td>Z2</td></tr>_x000D_
</tbody>_x000D_
</table>
_x000D_
You don't need js. Important is to set table height in [vh]