body{
    margin: 0px;
    background-color:aqua;
}
main{
    margin-left: 20 px;
    margin-right: 20 px;
    
    
    img{
        
        width: 500px;
        height: 250px;
        display: flex;
        margin-left:auto;
        margin-right:auto;
    }    
    
}
h1{
    text-align: center;
}
    
h2{
    text-align: center;
}
.navbar ul{
    list-style-type: none;
    background-color: hsl(0, 0%, 25%);
    padding: 0px;
    margin: 0px;
    overflow: hidden;
}
.navbar a{
    color: white;
    text-decoration: none;
    padding: 15px;
    display: block;
    text-align: center;
}
.navbar a:hover{
    background-color: hsl(0, 0%, 10%);
}
.navbar li{
    float: left;
}

<style>
    img{
        width: 500px;
        height: 250px;
        display: flex;
        align-items: center;
    }
</style>

footer{
    text-align: center;
}

* {

    box-sizing: border-box;
}

.clm {
     float: left;
     width:33.33%;
     padding: 5 px;

}

.row:: after {
    content:"";
    display: tables;
    clear:both;
}