Check out example codes for "scroll tbody fixed thead". It will help you in understanding the concepts better.

Code Example 1

table {
  width: 100%;
}

table, td {
  border-collapse: collapse;
  border: 1px solid #000;
}

thead {
  display: table; /* to take the same width as tr */
  width: calc(100% - 17px); /* - 17px because of the scrollbar width */
}

tbody {
  display: block; /* to enable vertical scrolling */
  max-height: 200px; /* e.g. */
  overflow-y: scroll; /* keeps the scrollbar even if it doesn't need it; display purpose */
}

th, td {
  width: 33.33%; /* to enable "word-break: break-all" */
  padding: 5px;
  word-break: break-all; /* 4. */
}

tr {
  display: table; /* display purpose; th's border */
  width: 100%;
  box-sizing: border-box; /* because of the border (Chrome needs this line, but not FF) */
}

td {
  text-align: center;
  border-bottom: none;
  border-left: none;
}

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