Using the WP flexbox grid

.wp-block-post-template {
    list-style: none;
    margin-bottom: 0;
    margin-top: 0;
    max-width: 100%;
    padding: 0;
}
.wp-block-post-template.is-flex-container {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    gap: 1.25em;
}
.wp-block-post-template.is-flex-container li {
    margin: 0;
    width: 100%;
}
@media (min-width: 600px)
.wp-block-post-template.is-flex-container.is-flex-container.columns-3>li {
    width: calc(33.33333% - 0.83333em);
}