<div id="wrap">
  <div id="header"></div>
  <div id="nav"></div>
  <div id="aside"></div>
  <div id="section_a"></div>
  <div id="section_b"></div>
  <div id="section_c"></div>
  <div id="footer"></div>    
</div>

* {
    padding: 0;
    margin: 0;
}
body {
    background-color: #E1F5FE;
}
#wrap {
    display: grid;
    width: 1200px;
    margin: 0 auto;

    grid-template-areas: 
        "header header"
        "nav nav"
        "aside section_a"
        "aside section_b"
        "aside section_c"
        "footer footer";
    grid-template-columns: 30% 70%; 
    grid-template-rows: 100px 100px 260px 260px 260px 100px;
}
#header {
    grid-area: header;
    background-color: #B3E5FC;
}
#nav {
    grid-area: nav;
    background-color: #81D4FA;
}
#aside {
    grid-area: aside;
    background-color: #4FC3F7;
}
#section_a {
    grid-area: section_a;
    background-color: #29B6F6;
}
#section_b {
    grid-area: section_b;
    background-color: #03A9F4;
}
#section_c {
    grid-area: section_c;
    background-color: #039BE5;
}
#footer {
    grid-area: footer;
    background-color: #0288D1;
}
@media (max-width: 1220px){
    #wrap {
        width: 96%;
        grid-template-areas: 
            "header header header"
            "nav nav nav"
            "aside section_a section_a"
            "aside section_b section_c"
            "footer footer footer";
        grid-template-columns: 25% 37.5% 37.5%; 
        grid-template-rows: 100px 100px 260px 520px 100px;
    }
}   
@media (max-width: 768px){
    #wrap {
        width: 100%;
        grid-template-areas: 
            "header header"
            "nav nav"
            "aside section_a"
            "aside section_b"
            "footer footer";
        grid-template-columns: 30% 70%; 
        grid-template-rows: 100px 100px 390px 390px 100px;
    }
    #section_c {
        display: none;
    }
}
@media (max-width: 480px){
    #wrap {
        grid-template-areas: 
            "header"
            "nav"
            "aside"
            "section_a"
            "section_b"
            "footer";
        grid-template-columns: 100%; 
        grid-template-rows: 100px 100px 200px 430px 150px 100px;
    }
}