border-style

/* Keyword values */
border-top-style: none;
border-top-style: hidden;
border-top-style: dotted;
border-top-style: dashed;
border-top-style: solid;
border-top-style: double;
border-top-style: groove;
border-top-style: ridge;
border-top-style: inset;
border-top-style: outset;

/* vertical | horizontal */
border-style: dotted solid;

/* top | horizontal | bottom */
border-style: hidden double dashed;

/* top | right | bottom | left */
border-style: none solid dotted dashed;

/* Global values */
border-style: inherit;
border-style: initial;
border-style: unset;

La propiedad border-style se puede especificar usando uno, dos, tres o cuatro valores.

• Cuando se especifica un valor, se aplica el mismo estilo a los cuatro lados.
• Cuando se especifican dos valores, el primer estilo se aplica a la parte superior e inferior, el segundo a la izquierda y a la derecha
• Cuando se especifican tres valores, el primer estilo se aplica a la parte superior, el segundo a la izquierda y derecha, el tercero a la parte inferior.
• Cuando se especifican cuatro valores, los estilos se aplican a la parte superior, derecha, inferior e izquierda en ese orden (en el sentido de las agujas del reloj).

Cada valor es una palabra clave elegida de la siguiente lista.

<br-style>

Describe el estilo del borde. Puede tener los siguientes valores:

none		Like the hidden keyword, displays no border. Unless a background-image is set, the calculated value of border-top-width will be 0, even if the specified value is something else. In the case of table cell and border collapsing, the none value has the lowest priority: if any other conflicting border is set, it will be displayed.
hidden		Like the none keyword, displays no border. Unless a background-image is set, the calculated value of border-top-width will be 0, even if the specified value is something else. In the case of table cell and border collapsing, the hidden value has the highest priority: if any other conflicting border is set, it won't be displayed.
dotted		Displays a series of rounded dots. The spacing of the dots is not defined by the specification and is implementation-specific. The radius of the dots is half the calculated border-top-width.
dashed		Displays a series of short square-ended dashes or line segments. The exact size and length of the segments are not defined by the specification and are implementation-specific.
solid		Displays a single, straight, solid line.
double		Displays two straight lines that add up to the pixel size defined by border-width or border-top-width.
groove		Displays a border with a carved appearance. It is the opposite of ridge.
ridge		Displays a border with an extruded appearance. It is the opposite of groove.
inset		Displays a border that makes the element appear embedded. It is the opposite of outset. When applied to a table cell with border-collapse set to collapsed, this value behaves like groove.
outset		Displays a border that makes the element appear embossed. It is the opposite of inset. When applied to a table cell with border-collapse set to collapsed, this value behaves like ridge.

border-style = 
  <line-style>{1,4}  

<line-style> = 
  none    |
  hidden  |
  dotted  |
  dashed  |
  solid   |
  double  |
  groove  |
  ridge   |
  inset   |
  outset  

A continuación, se muestra un ejemplo de todos los valores de propiedad.

HTML

<table>
  <tr>
    <td class="b1">none</td>
    <td class="b2">hidden</td>
    <td class="b3">dotted</td>
    <td class="b4">dashed</td>
  </tr>
  <tr>
    <td class="b5">solid</td>
    <td class="b6">double</td>
    <td class="b7">groove</td>
    <td class="b8">ridge</td>
  </tr>
  <tr>
    <td class="b9">inset</td>
    <td class="b10">outset</td>
  </tr>
</table>

CSS

/* Define look of the table */
table {
  border-width: 3px;
  background-color: #52e396;
}
tr,
td {
  padding: 2px;
}

/* border-style example classes */
.b1 {
  border-style: none;
}
.b2 {
  border-style: hidden;
}
.b3 {
  border-style: dotted;
}
.b4 {
  border-style: dashed;
}
.b5 {
  border-style: solid;
}
.b6 {
  border-style: double;
}
.b7 {
  border-style: groove;
}
.b8 {
  border-style: ridge;
}
.b9 {
  border-style: inset;
}
.b10 {
  border-style: outset;
}

Output

• The border-related shorthand CSS properties: border, border-width, border-color, border-radius