<table>
  <tr>
    <td rowspan="2">Mon hoc</td>
    <td colspan="7">Thoi khoa bieu</td>
  </tr>
  <tr>
    <td>T2</td>
    <td>T3</td>
    <td>T4</td>
    <td>T5</td>
    <td>T6</td>
    <td>T7</td>
    <td>CN</td>
  </tr>
  <tr>
    <td>Mon toan</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>O</td>
  </tr>
  <tr>
    <td>Mon van</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>O</td>
  </tr>
  <tr>
    <td>Mon toan</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>O</td>
  </tr>
  <tr>
    <td>Mon van</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>O</td>
  </tr>
  <tr>
    <td>Mon toan</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>X</td>
    <td>O</td>
    <td>O</td>
  </tr>
</table>
table{
/*  border: 1px solid #000;
  border-spacing: 0;*/
  border-collapse: collapse;
}
td{
  border: 1px solid #000;
  padding: 1em;
}
tr:first-child td{
  background-color: grey;
  font-weight: bold;
  text-align: center;
  color: #fff;
}

tr:nth-child(2) td{
  background-color: blue;
  color: white;
}

/* tr:nth-child(n+3):nth-child(-n+7):nth-child(2n+1) td:nth-child(1){
  background-color: yellow;
  font-weight: bold;
}

tr:nth-child(n+3):nth-child(-n+7) td:nth-child(2n){
  background-color: green;
  color: white;
}

tr:nth-child(n+3):nth-child(-n+7) td:nth-child(2n+1):not(:nth-child(1)){
  background-color: orange;
  color: white;
}

tr:nth-child(n+3):nth-child(-n+7) td:nth-child(8){
  background-color: red;
  color: white;
} */

tr:nth-child(odd):nth-child(n+3){
  background-color: #ccc;
}
tr:nth-child(n+3):nth-child(2n){
  background-color: #eee;
}
tr:not(:nth-child(-n+2)) td:nth-child(even){
  color: green;
}
tr:nth-child(n+3) td:nth-child(odd):not(:first-child){
  color: purple;
}
tr:nth-child(n+2) td:last-child{
  color: red;
}
tr:nth-child(n+3) td:first-child{
  font-weight: bold;
}

External CSS

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