<ul class="galerie">
<li><img src="image.jpg" alt></li>
...
</ul>
*{box-sizing:border-box}
.galerie {
max-width:80%;
display: grid;
grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
gap: 1rem;
margin:2rem auto;
padding: 0;
list-style-type: none;
}
.galerie img{
display:block;
width: 100%;
aspect-ratio: 3/2;
object-fit: cover;
}