这很简单，只需添加：

.primary {
  grid-row: span 2;
}

虽然很明显我选择了添加一个CSS类到您想要获得焦点的元素，为了做到这一点：
x一个一个一个一个x一个一个二个x
JS Fiddle demo .
当然，上述内容可以在不添加类名和简单地指定:nth-child()元素的情况下实现：

/* or .container > div:first-child: */
.container > div:nth-child(1) {
  grid-row: span 2;
}

.container {
  display: grid;
  width: 800px;
  grid-template-columns: repeat(3, 1fr);

  grid-template-rows: repeat(2, 1fr);
  grid-gap: 1rem;
}

/* OTHER STYLES */

body {
  background-color: #3b404e;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.item {
  height: 100px;
  background-color: #1EAAFC;
  background-image: linear-gradient(130deg, #6C52D9 0%, #1EAAFC 85%, #3EDFD7 100%);
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.19), 0 6px 6px rgba(0, 0, 0, 0.23);
  color: #fff;
  border-radius: 4px;
  border: 6px solid #171717;
}

.item1 {
  height: 250px;
}

/* or .container > div:first-child: */
.container > div:nth-child(1) {
  grid-row: span 2;
}

<div class="container">
  <div class="item item1 primary"></div>
  <div class="item item2"></div>
  <div class="item item3"></div>
  <div class="item item4"></div>
  <div class="item item5"></div>
</div>

JS Fiddle demo .
参考文献：

• grid-row .

第一件事你不能只有两行。网格给出了一个结构。
有3行，这是可能的

.container {
  display: grid;
  width: 800px;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  grid-gap: 1rem;
}

/* OTHER STYLES */

body {
  background-color: #3b404e;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.item {
  height: 100px;
  background-color: #1EAAFC;
  background-image: linear-gradient(130deg, #6C52D9 0%, #1EAAFC 85%, #3EDFD7 100%);
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.19), 0 6px 6px rgba(0, 0, 0, 0.23);
  color: #fff;
  border-radius: 4px;
  border: 6px solid #171717;
}

.item1 {
  height: 250px;
  grid-area: 1 / 1 / 3 / 2;
}

.item2 {
  grid-area: 3 / 1 / 4 / 2;
}

.item3 {
  grid-area: 1 / 2 / 2 / 3;
}

.item4 {
  grid-area: 1 / 3 / 2 / 4;
}

.item5 {
  height: 250px;
  grid-area: 2 / 2 / 4 / 3;
}

.item6 {
  height: 250px;
  grid-area: 2 / 3 / 4 / 4;
}

<div class="container">
  <div class="item item1"></div>
  <div class="item item2"></div>
  <div class="item item3"></div>
  <div class="item item4"></div>
  <div class="item item5"></div>
  <div class="item item6"></div>
</div>

这是使用每个项目的网格区域位置执行此操作的一种方法
也可以对span执行相同的操作

另一个解决这个问题的方法是...

.container {
  display: grid;
  width: 800px;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(2, 1fr);
  grid-gap: 1rem;
}

/* OTHER STYLES */

body {
  background-color: #3b404e;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
    box-sizing:border-box;
}

.item {
  height: 100px;
  background-color: #1EAAFC;
  background-image: linear-gradient(130deg, #6C52D9 0%, #1EAAFC 85%, #3EDFD7 100%);
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.19), 0 6px 6px rgba(0, 0, 0, 0.23);
  color: #fff;
  border-radius: 4px;
  border: 6px solid #171717;
}

.item1 {
    grid-column-start: 1;
    grid-column-end: 2;
    grid-row-start: 1;
    grid-row-end: 3;
    height: 250px;
}
.item4 {
    grid-column-start: 2;
    grid-column-end: 3;
    grid-row-start: 2;
    grid-row-end: 3;
        
}
.item5 {
    grid-column-start: 3;
    grid-column-end: 4;
    grid-row-start: 2;
    grid-row-end: 3;
}

<div class="container">
  <div class="item item1">item 1</div>
  <div class="item item2">item 2</div>
  <div class="item item3">item 3</div>
  <div class="item item4">item 4</div>
  <div class="item item5">item 5</div>
  </div>