Borders

<div id="first">
  Grey borders on top and bottom, red borders on right and left.
</div>

div {
  padding: 10px;
  margin: 10px;
}
#first {
  border-style: solid;
  border-color: grey red;
}

<div id="first">
  Blue border on top, transparent border on right and left, green border at the bottom.
</div>

div {
  padding: 10px;
  margin: 10px;
}
#first {
  border-style: dashed;
  border-color: blue transparent green;
}

<div id="first">
  Blue border on top, red border on right, green border at the bottom and yellow border on the left.
</div>

div {
  padding: 10px;
  margin: 10px;
}
#first {
  border-style: solid;
  border-color: blue red green yellow;
}