Horizontal border across entire row of CSS GRID

Question

I need to use a grid layout but also need a horizontal line separating each row.

The only thing I've been able to find is applying a border to each cell, but this only works if there are enough cells to fill each row.

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 100px);
}

.box {
  border-bottom: 2px solid #ffa94d;
  padding: 1em;
}

<div class="wrapper">
  <div class="box">One</div>
  <div class="box">Two</div>
  <div class="box">Three</div>
  <div class="box">Four</div>
</div>

Is there a way to fix the above so that the entire row has a border?

Answer 1

Add a grid-gap equal to the width of your border then consider gradient to achieve this:

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 100px);
  grid-row-gap:2px;
  background:
    repeating-linear-gradient(to bottom,
      transparent 0,
      transparent 100px,
      #ffa94d 100px,
      #ffa94d 102px /*+2px here*/
    );
}

.box {
  padding: 1em;
}

<div class="wrapper">
  <div class="box">One</div>
  <div class="box">Two</div>
  <div class="box">Three</div>
  <div class="box">Four</div>
</div>

Another idea is to consider a pseudo-element that you add to the 1st,4th,7th .. (3n + 1)th element:

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 100px);
  overflow:hidden;
}

.box {
  position:relative;
  padding: 1em;
}
.box:nth-child(3n + 1)::after {
  content:"";
  position:absolute;
  bottom:0px;
  left:0;
  width:100vw;
  height:2px;
  background:#ffa94d;
}

<div class="wrapper">
  <div class="box">One</div>
  <div class="box">Two</div>
  <div class="box">Three</div>
  <div class="box">Four</div>
</div>

Answer 2

Imagine your table as a collection of cells (much like an excel spreadsheet). You can create a simple cell class that you append to each of your grid items to manipulate the cells without affecting the table data itself. Consider:

.wrapper {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  
  grid-row-gap: 20px;
}


.cell {
  position: relative;
  border-bottom: 2px solid #ffa94d;
}

<div class="wrapper">
  <!-- Here is your first row -->
  <div class="cell">One</div>
  <div class="cell">Two</div>
  <div class="cell">Three</div>

  <!-- Here is your second row -->
  <div class="cell">Four</div>
  <!-- You can extend the line by the number of cells per row -->
  <div class="cell"></div>
  <div class="cell"></div>
  
  <!-- Organize your html into row groups to easily visualize them -->
  <!-- This will produce a blank row with no line -->
  <div></div>
  <div>-- blank row --</div>
  <div></div>
  
  <!-- You can also control where the line begins and ends -->
  <div class="box cell">First Column Only</div>
  <div></div> <!-- No cells here.. We just want to underline the first column -->
  <div></div>
  
  <!-- 2nd and 3rd columns only -->
  <div></div>
  <div class="cell">Second Column</div>
  <div class="cell">Third Column</div>
  
  
  
</div>

Note that I only used a grid-row-gap. If you introduce a grid-gap, or a grid-column-gap, your lines will be broken at the column gaps (this may be the desired effect in some cases).

It is true that this is a more involved method of controlling the horizontal lines separating the grid and less "programmatic" and more micro-management-esque but, it does provide great control over introducing the lines into your grid.

The other answers were great options too! I just wanted to provide my two cents.