body{
    margin:0;
    margin-top:50px;
}
header{
    display:flex;
    position:fixed;
    top:0;
    left:0;
    right:0;
    height:50px;
    line-height:50px;
    background-color:purple;
}
header *{
    display:inline;
}
header li{
    margin-left:20px;
}
header a{
    text-decoration:none;
    color:red;
}
section{
    height:100vh;
    border:1px solid black;
    display:flex;
    justify-content:center;
    text-align:center;
    background-repeat:no-repeat;
    background-position:center;
    background-size:cover;
    align-items:center;
}
#contact a{
    text-decoration:none;
    color:black;
}
#contact li{
    list-style-type:none;
}
#home{
    background-image:
    linear-gradient(rgba(255,255,255,0.8),rgba(255,255,255,0.8)),url('iphone.jpg')
}
#service{
    background-image:
    linear-gradient(rgba(255,255,255,0.8),rgba(255,255,255,0.8)),url('iphone.jpg')
}
#product{
    background-image:
    linear-gradient(rgba(255,255,255,0.8),rgba(255,255,255,0.8)),url('iphone.jpg')
}
#contact{
    background-image:
    linear-gradient(rgba(255,255,255,0.8),rgba(255,255,255,0.8)),url('iphone.jpg')
}
nav{
    text-align-last:center;
}
section{
    text-align:center;
}