border-collapse

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The border-collapse CSS property sets whether cells inside a

have shared or separate borders.

Try it

border-collapse: collapse;

border-collapse: separate;
Cell 1.1 Cell 1.2
Cell 2.1 Cell 2.2
Cell 3.1 Cell 3.2 
table {
  width: 15rem;
  table-layout: fixed;
}

td {
  border: 5px solid;
  border-color: crimson dodgerblue orange limegreen;
  padding: 0.75rem;
}

When cells are collapsed, the border-style value of inset behaves like ridge, and outset behaves like groove.

When cells are separated, the distance between cells is defined by the border-spacing property.