Check out example codes for "grid css". It will help you in understanding the concepts better.

Code Example 1

<!DOCTYPE html>
<html>
<head>
<style>
.grid-container {
  display: grid;
  grid-template-columns: auto auto auto;
  background-color: #2196F3;
  padding: 10px;
}
.grid-item {
  background-color: rgba(255, 255, 255, 0.8);
  border: 1px solid rgba(0, 0, 0, 0.8);
  padding: 20px;
  font-size: 30px;
  text-align: center;
}
</style>
</head>
<body>

  <div class="grid-container">
    <div class="grid-item">1</div>
    <div class="grid-item">2</div>
    <div class="grid-item">3</div>  
    <div class="grid-item">4</div>
    <div class="grid-item">5</div>
    <div class="grid-item">6</div>  
    <div class="grid-item">7</div>
    <div class="grid-item">8</div>
    <div class="grid-item">9</div>  
  </div>

</body>

Code Example 2

.item-a {
  grid-area: header;
}
.item-b {
  grid-area: main;
}
.item-c {
  grid-area: sidebar;
}
.item-d {
  grid-area: footer;
}

.container {
  display: grid;
  grid-template-columns: 50px 50px 50px 50px;
  grid-template-rows: auto;
  grid-template-areas: 
    "header header header header"
    "main main . sidebar"
    "footer footer footer footer";
}

Code Example 3

repeat(/*Number of repeats*/, /*Code to be repeated*/)

.gridContainer {
	grid-template-columns: repeat(4, 100px); /*Creates 4 columns, each 100px in width*/
	grid-template-rows: repeat(2, 250px); /*Creates 2 rows, each 250px in height*/
}

Code Example 4

.container {
  display: grid | inline-grid;
}

Code Example 5

/* grid-column: <start> / <end>;  */
/* grid-row: <start> / span <length>;  */
/* i.e */
grid-column: 3 / span 2;
grid-row: 2 / 4;
grid-row: 4;

Code Example 6

grid-row-start:    2;
grid-row-end:      3;
grid-column-start: 2;
grid-column-end:   3;

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