img {
width: 300px;
}

html {
text-align: center;
background: slateblue;
font-family: Arial;
}

h1 {
font-size: 60px;
}

h2 {
font-size: 30px;
}

body {
width: 900px;
margin: 0 auto;
background: slategrey;
padding: 20px;
}

ol,   {
text-align: left;
List-style-position: inside;
 }

ol{
padding: 0;
}

ol, ul {
padding:0;
}

ul li {
list-style: none;
display: inline-block;
width: 100px;

}

li a {
display: block;
background: slateblue;
color: black;
text-decoration: none;
}

li a:hover {
background: white;
transition: background 0.5s;
}








div#gallery {
display: gried;
grid-template-columns: 1fr 1fr 1fr 1fr;
grid-template-rows: 225px 225px;
grid-gap: 20px;
}

#gallery img {
width: 100%;
height: 100%;
object-fit: cover;
}