give div border code example

Example 1: make border to div

border: 2px solid black

Example 2: css border top

.topBorder {
  /*        width style color  */
  border-top: 5px solid black;
}

Example 3: border width css

#some-div {
  /* [WIDTH] [FILL MODE] [COLOR] */
  border: 5px solid #f00; 
  
  /* draws solid a red line of 5px
  between the padding (inside the div)
  and the margin (outside the div) */
}