layout.css

header{
    position: fixed;
    top:0;
    left: 0;
    margin:0 auto 0 auto;
    background-color: #ccc;
    width: 100%;
    height: 120px;  
    text-align:center;
    z-index: 4;
    
}
h1{
    font-family:'Helvetica',sans-serif;
    color: #000000;
    font-size: 36px;
    margin: 32px auto auto auto;
    
}
main{
    position: float;
    display: flex;
    align-items:stretch;
    max-width: 900px;
    margin: 130px auto auto auto;
    z-index: 3;
}
main > div{
    background-color:#ccc;
    min-width:250px;
    margin-left: 5px;
    margin-right: 5px;
    flex-grow: 1;
    
}
main > div > p{
    margin: 15px;
    font-family: serif;
    font-size: 16px;
    color: rgb(0,0,0);
    line-height: 1.2;
    max-height: 590px;
    overflow:hidden;
}
footer{
    display: flex;
    position: float;
    top:140px;
    justify-content: center;
    max-width: 900px;
    margin: 15px auto;
}
footer > div{
    height: 90px;
    min-width: 330px;
    background-color: #ccc;
    margin: auto 5px;
}
footer > div > p{
    height: 65px;
    overflow: hidden;
    margin:auto 20px;
    padding-top: 15px;
    font-family: serif;
    font-size: 14px;
    color: rgb(0,0,0);
    line-height: 1.2;
    text-align: justify;
}

@media (max-width: 800px){
    main{
        flex-wrap: wrap;
        flex-direction: column;
        margin-bottom: 15px;
}
    main > div{
        margin: 5px;
    }
    main > div > p{
        max-height: 250px;   
    }
}
@media (max-width: 690px){
    footer{
        flex-wrap: wrap;
        margin: 0 auto;
        max-width: 430px;
    }
    footer > div{
        margin: 5px; 
        height: 30px;
    }
    footer > div > p{
        max-height: 18px;
        padding-top: 6px;
    }
}