style.css

.zone {
    cursor:pointer;
    color:#FFF;
    font-size:2em;
    border-radius:4px;
    border:1px solid #bbb;
    transition: all 0.3s linear;
}

html, body{
    margin: auto 0;
}

.zone:hover {
    -webkit-box-shadow:rgba(0,0,0,0.8) 0px 5px 15px, inset rgba(0,0,0,0.15) 0px -10px 20px;
    -moz-box-shadow:rgba(0,0,0,0.8) 0px 5px 15px, inset rgba(0,0,0,0.15) 0px -10px 20px;
    -o-box-shadow:rgba(0,0,0,0.8) 0px 5px 15px, inset rgba(0,0,0,0.15) 0px -10px 20px;
    box-shadow:rgba(0,0,0,0.8) 0px 5px 15px, inset rgba(0,0,0,0.15) 0px -10px 20px;
}

.main-nav{
    display: flex;
    list-style:none;
    font-size: 0.7em;
    margin:0;
}

.container{
    display: flex;
    align-items: center;
    justify-content: center;
    height: 50vh;
}
@media only screen and (max-width: 600px) {
    .main-nav{
        font-size: 0.5em;
        padding:0;
    }
}

.push{
    margin-left: auto;
}

li{

    padding: 25px;
}

a{
    color:#f5f5f6;
    text-decoration: none;
}

/* GRID */
.grid-wrapper{
    display: grid;
    grid-gap: 20px;
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
}
.box > img{
    width: 100%;
}

.box{
    background-color: #444;
    padding: 130px;
    margin:20px;
}

footer{
    text-align: center;
}

/*https://paulund.co.uk/how-to-create-shiny-css-buttons*/
/***********************************************************************
 *  Green Background
 **********************************************************************/
.green{
    background: #56B870; /* Old browsers */
    background: -moz-linear-gradient(top, #56B870 0%, #a5c956 100%); /* FF3.6+ */
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#56B870), color-stop(100%,#a5c956)); /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(top, #56B870 0%,#a5c956 100%); /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(top, #56B870 0%,#a5c956 100%); /* Opera 11.10+ */
    background: -ms-linear-gradient(top, #56B870 0%,#a5c956 100%); /* IE10+ */
    background: linear-gradient(top, #56B870 0%,#a5c956 100%); /* W3C */
}

/***********************************************************************
 *  Red Background
 **********************************************************************/
.red{
    background: #C655BE; /* Old browsers */
    background: -moz-linear-gradient(top, #C655BE 0%, #cf0404 100%); /* FF3.6+ */
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#C655BE), color-stop(100%,#cf0404)); /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(top, #C655BE 0%,#cf0404 100%); /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(top, #C655BE 0%,#cf0404 100%); /* Opera 11.10+ */
    background: -ms-linear-gradient(top, #C655BE 0%,#cf0404 100%); /* IE10+ */
    background: linear-gradient(top, #C655BE 0%,#cf0404 100%); /* W3C */
}

/***********************************************************************
 *  Yellow Background
 **********************************************************************/
.yellow{
    background: #F3AAAA; /* Old browsers */
    background: -moz-linear-gradient(top, #F3AAAA 0%, #febf04 100%); /* FF3.6+ */
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#F3AAAA), color-stop(100%,#febf04)); /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(top, #F3AAAA 0%,#febf04 100%); /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(top, #F3AAAA 0%,#febf04 100%); /* Opera 11.10+ */
    background: -ms-linear-gradient(top, #F3AAAA 0%,#febf04 100%); /* IE10+ */
    background: linear-gradient(top, #F3AAAA 0%,#febf04 100%); /* W3C */
}

/***********************************************************************
 *  Blue Background
 **********************************************************************/
.blue{
    background: #7abcff; /* Old browsers */
    background: -moz-linear-gradient(top, #7abcff 0%, #60abf8 44%, #4096ee 100%); /* FF3.6+ */
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#7abcff), color-stop(44%,#60abf8), color-stop(100%,#4096ee)); /* Chrome,Safari4+ */
    background: -webkit-linear-gradient(top, #7abcff 0%,#60abf8 44%,#4096ee 100%); /* Chrome10+,Safari5.1+ */
    background: -o-linear-gradient(top, #7abcff 0%,#60abf8 44%,#4096ee 100%); /* Opera 11.10+ */
    background: -ms-linear-gradient(top, #7abcff 0%,#60abf8 44%,#4096ee 100%); /* IE10+ */
    background: linear-gradient(top, #7abcff 0%,#60abf8 44%,#4096ee 100%); /* W3C */
}