HTML Table Borders
HTML tables can have borders of different styles and shapes.

How To Add a Border
To add a border, use the CSS border property on table, th, and td elements:
Example:

table, th, td {
  border: 1px solid black;
}

Collapsed Table Borders
To avoid having double borders like in the example above, set the CSS border-collapse property to collapse.

This will make the borders collapse into a single border:
Example:

table, th, td {
  border: 1px solid black;
  border-collapse: collapse;
}

Style Table Borders
If you set a background color of each cell, and give the border a white color (the same as the document background), you get the impression of an invisible border:
Example:

table, th, td {
  border: 1px solid white;
  border-collapse: collapse;
}
th, td {
  background-color: #96D4D4;
}

Round Table Borders
With the border-radius property, the borders get rounded corners:

Example:

table, th, td {
  border: 1px solid black;
  border-radius: 10px;
}

Skip the border around the table by leaving out table from the css selector:

Example:

th, td {
  border: 1px solid black;
  border-radius: 10px;
}

Dotted Table Borders
With the border-style property, you can set the appearance of the border.

The following values are allowed:

• dotted
• dashed
• solid
• double
• groove
• ridge
• inset
• outset
• none
• hidden Example:

 th, td {
  border-style: dotted;
}

** Border Color**
With the border-color property, you can set the color of the border.

Example:

 th, td {
  border-color: #96D4D4;
}

References:
https://www.w3schools.com/html/html_table_borders.asp
https://www.geeksforgeeks.org/html/html-table-border-attribute/