style.css

/* desktop */
.container {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  grid-template-rows: 50px 50px 1fr 200px;
  grid-template-areas: 
    "navigation navigation navigation navigation navigation"
    ". header header header ."
    ". content content content ."
    "footer footer footer footer footer";
  grid-gap: 0.5em;
}

/* tablet */
@media screen and (max-width: 786px) {
  .container {
    display: grid;
    grid-template-columns: 50px 1fr 1fr 50px;
    grid-template-rows: 70px 1fr 150px;
    grid-template-areas: 
      "navigation navigation header header"
      ". content content ."
      "footer footer footer footer";
    grid-gap: 0.25em;
  }
}

/* moblie */
@media screen and (max-width: 480px) {
  .container {
    display: grid;
    grid-template-columns: 20px 1fr 1fr 20px;
    grid-template-rows: 30px 1fr 100px;
    grid-template-areas: 
      "navigation navigation header header"
      ". content content ."
      "footer footer footer footer";
    grid-gap: 0.2em;
  }
}

.container > div.navigation, div.header, div.footer {
  background-color: aquamarine;
  padding: 0.5em;
  text-align: center;
}

.navigation {
  grid-area: navigation;
}

.header {
  grid-area: header;
}

.content {
  grid-area: content;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  grid-gap: 0.5em;
  background-color: lightgrey;
  padding: 0.5em;
}

@media screen and (max-width: 786px) {
  .content {
    grid-area: content;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    grid-template-rows: auto;
    grid-gap: 0.5em;
    background-color: lightgrey;
    padding: 1em;
  }
}

@media screen and (max-width: 480px) {
  .content {
    grid-area: content;
    display: grid;
    grid-template-columns: 1fr;
    grid-template-rows: auto;
    grid-gap: 0.5em;
    background-color: lightgrey;
    padding: 1em;
  }
}

.footer {
  grid-area: footer;
}

.content .box {
  color: white;
  background-color: blue;
  padding: 1em;
}