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HTML 

              
                <header class="header">
  <h1>CSS Grid Layout</h1>
  <h2>With @support flexbox fallback.</h2>
</header>

<div class="grid ">
  <div class="item" tabindex="1">
    <div class="box">
      <div class="diamond"><span>1</span></div>
      <div class="tooltip">grid-area: hero</div>
    </div>
  </div>
  <div class="item" tabindex="2">
    <div class="box">
      <div class="diamond"><span>2</span></div>
      <div class="tooltip">grid-area: big</div>
    </div>
  </div>
  <div class="item" tabindex="3">
    <div class="box">
      <div class="diamond"><span>3</span></div>
      <div class="tooltip">grid-area: medium</div>
    </div>
  </div>
  <div class="item" tabindex="4">
    <div class="box">
      <div class="diamond"><span>4</span></div>
      <div class="tooltip">grid-area: medium</div>
    </div>
  </div>
  <div class="item" tabindex="5">
    <div class="box">
      <div class="diamond"><span>5</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="6">
    <div class="box">
      <div class="diamond"><span>6</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="7">
    <div class="box">
      <div class="diamond"><span>7</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="8">
    <div class="box">
      <div class="diamond"><span>8</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="9">
    <div class="box">
      <div class="diamond"><span>9</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="10">
    <div class="box">
      <div class="diamond"><span>10</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="11">
    <div class="box">
      <div class="diamond"><span>11</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="12">
    <div class="box">
      <div class="diamond"><span>12</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="13">
    <div class="box">
      <div class="diamond"><span>13</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
  <div class="item" tabindex="14">
    <div class="box">
      <div class="diamond"><span>14</span></div>
      <div class="tooltip">grid-area: small</div>
    </div>
  </div>
</div>
!

CSS 

              
                @supports (display: grid) {

  .grid {
    display: grid;
    grid-gap: 1.5vw;
    min-height: 100vh;
    padding: 1.5vw;
  }

  .grid {
    grid-template-columns: repeat(2, 1fr);
    grid-template-rows: 50vh 30vh repeat(7, minmax(20vh, 1fr));
    grid-template-areas:
      "hero   hero"
      "big1   big1"
      "med1   med1"
      "med2   med2"
      "small1 small2"
      "small3 small4"
      "small5 small6"
      "small7 small8"
      "small9 small10";
  }

  @media screen and (min-width: 750px) {
    .grid {
      grid-template-columns: repeat(5, 1fr);
      grid-template-rows: repeat(5, 25vh);
      grid-template-areas:
        "hero   hero   hero   med1   med1"
        "hero   hero   hero   med2   med2"
        "big1   big1   big1   big1   big1"
        "small1 small2 small3 small4 small5"
        "small6 small7 small8 small9 small10";
    }
  }

  @media screen and (min-width: 1400px) {
    .grid {
      grid-template-columns: repeat(6, 1fr);
      grid-template-rows: auto;
      grid-template-areas:
      "small1 hero   hero hero med1   med1"
      "small2 hero   hero hero med2   med2"
      "small3 small5 big1 big1 small7 small8"
      "small4 small6 big1 big1 small9 small10";
    }
  }

  .grid .item:nth-child(1)  { grid-area: hero; }
  .grid .item:nth-child(2)  { grid-area: big1; }
  .grid .item:nth-child(3)  { grid-area: med1; }
  .grid .item:nth-child(4)  { grid-area: med2; }
  .grid .item:nth-child(5)  { grid-area: small1; }
  .grid .item:nth-child(6)  { grid-area: small2; }
  .grid .item:nth-child(7)  { grid-area: small3; }
  .grid .item:nth-child(8)  { grid-area: small4; }
  .grid .item:nth-child(9)  { grid-area: small5; }
  .grid .item:nth-child(10) { grid-area: small6; }
  .grid .item:nth-child(11) { grid-area: small7; }
  .grid .item:nth-child(12) { grid-area: small8; }
  .grid .item:nth-child(13) { grid-area: small9; }
  .grid .item:nth-child(14) { grid-area: small10; }

}

/* flexbox fallback is the browser does not support display:grid */
@supports not (display: grid) {

  .grid {
    display: flex;
    flex-flow: row wrap;
    min-height: 100vh;
    padding: 0.75vw;
  }

  .grid .item {
    min-height: 20vh;
    margin: 0.75vw;
  }

  .grid .item:nth-child(1)  { flex: 0 1 calc(100% - 1.5vw); height: 50vh; }
  .grid .item:nth-child(2)  { flex: 0 1 calc(100% - 1.5vw); height: 30vh; }
  .grid .item:nth-child(3)  { flex: 0 1 calc(100% - 1.5vw); }
  .grid .item:nth-child(4)  { flex: 0 1 calc(100% - 1.5vw); }
  .grid .item:nth-child(5)  { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(6)  { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(7)  { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(8)  { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(9)  { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(10) { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(11) { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(12) { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(13) { flex: 0 1 calc(50% - 1.5vw); }
  .grid .item:nth-child(14) { flex: 0 1 calc(50% - 1.5vw); }

  @media screen and (min-width: 750px) {
    .grid .item:nth-child(1)  { flex: 0 1 calc(60% - 1.5vw); }
    .grid .item:nth-child(2)  { flex: 0 1 calc(40% - 1.5vw); height: 50vh; }
  }

  @media screen and (min-width: 1400px) {
    .grid .item:nth-child(1)  { flex: 0 1 calc(60% - 1.5vw); }
    .grid .item:nth-child(2)  { flex: 0 1 calc(40% - 1.5vw); }
    .grid .item:nth-child(3)  { flex: 0 1 calc(50% - 1.5vw); }
    .grid .item:nth-child(4)  { flex: 0 1 calc(50% - 1.5vw); }
    .grid .item:nth-child(5)  { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(6)  { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(7)  { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(8)  { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(9)  { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(10) { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(11) { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(12) { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(13) { flex: 0 1 calc(25% - 1.5vw); }
    .grid .item:nth-child(14) { flex: 0 1 calc(25% - 1.5vw); }
  }

}

/* Styles, just for fun */

*,*:before,*:after {
  box-sizing: border-box;
}

body {
  margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  background: #29343d;
}

@supports not (display: grid) {
  body:before {
    content: 'Sorry, seems like your browser doesn\'t support display: grid. Below is the flexbox fallback.';
    display: block;
    padding: 2rem 2rem 0;
    color: #ffffff;
    text-align: center;
  }
}

.header {
  margin: 10vh 1.5vw;
  text-align: center;
  color: #cedfe9;
}

.header h1,
.header h2 {
  margin: 0;
  text-transform: uppercase;
  letter-spacing: 0.2em;
  line-height: 1;
}

.header h1 {
  position: relative;
  padding-bottom: 0.5em;
  color: #ffffff;
  font-size: 2rem;
}

.header h2 {
  font-weight: normal;
  font-size: 0.875rem;
}

@media screen and (min-width: 750px) {

  .header h1 {
    font-size: 3.75rem;
  }

  .header h2 {
    font-weight: normal;
    font-size: 1.125rem;
    letter-spacing: 0.5em;
  }
}

@media screen and (min-width: 1400px) {

  .header h1 {
    font-size: 6rem;
  }

  .header h2 {
    font-weight: normal;
    font-size: 1.5rem;
  }
}

.box {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100%;
}

.diamond {
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
  z-index: 2;
  width: 50px;
  height: 50px;
  border-radius: 5px;
  border: 1px solid #ffffff;
  box-shadow: 1px 1px 0px rgba(0,0,0,0.2);
  background-image: linear-gradient(to top left, #ddd 0%, #fff 100%);
  text-align: center;
  transform-origin: center;
  transform: rotateZ(45deg);
  transition: box-shadow 250ms, transform 250ms;
}

.diamond span {
  font-weight: bold;
  transform: rotateZ(-45deg)
}

.grid .item:hover .diamond,
.grid .item:focus .diamond {
  box-shadow: 2px 2px 2px rgba(0,0,0,0.2);
  transform:  rotateZ(45deg) scale(1.2);
}

.tooltip {
  position: absolute;
  z-index: 1;
  padding: 0.25rem 1rem;
  border-radius: 5px;
  background: #29343d;
  opacity: 0;
  color: #cedfe9;
  font-size: 0.875rem;
  transition: opacity 500ms, transform 500ms;
}

.tooltip:before {
  content: '';
  position: absolute;
  top: -9px;
  left: calc(50% - 10px);
  width: 0;
  height: 0;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  border-bottom: 10px solid #29343d;
}

.grid .item:hover .tooltip,
.grid .item:focus .tooltip {
  opacity: 1;
  transform: translateY(70px);
}

.grid .item {
  position: relative;
  padding: 1vw;
  background-position:  left bottom;
  background-size: 150% 100%;
  transition: background 500ms, outline 500ms;
  background-position: top left;
  outline: transparent;
}

.grid .item:hover,
.grid .item:focus {
  background-position: top right;
}

.grid .item:focus {
  outline: 2px solid #3eabfa;
}

.grid .item:nth-child(1)  { background-image: linear-gradient(45deg, #cbabfb 0%, #fb7ef6 60%); }
.grid .item:nth-child(2)  { background-image: linear-gradient(45deg, #fb7ef6 0%, #cbabfb 60%); }
.grid .item:nth-child(3)  { background-image: linear-gradient(45deg, #70c1fb 0%, #79ebe0 60%); }
.grid .item:nth-child(4)  { background-image: linear-gradient(45deg, #79ebe0 0%, #70c1fb 60%); }
.grid .item:nth-child(5),
.grid .item:nth-child(6),
.grid .item:nth-child(7),
.grid .item:nth-child(8),
.grid .item:nth-child(9),
.grid .item:nth-child(10),
.grid .item:nth-child(11),
.grid .item:nth-child(12),
.grid .item:nth-child(13),
.grid .item:nth-child(14) { background-image: linear-gradient(45deg, #feeeab 0%, #fb7eb3 60%); }
!

JS
!
999px

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