https://joshcollinsworth.com/adding-gutenberg-full-and-wide-width-image-support-to-your-wordpress-theme/
EDIT: Also add this code:
/* Maked gallery actually crop correctly*/
.pl-content-loop .wp-block-gallery.is-cropped .blocks-gallery-item img {
height: 100%;
}
/* Correctly adjusts full width image display */
.wp-block-image {
max-width: inherit;
}
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
/* Also these are the most current ones */
.alignfull {
width: 100vw;
margin-left: calc(50% – 50vw) !important;
}
.wp-block-cover .wp-block-cover__inner-container {
max-width: 1200px;
}
.alignwide {
width: calc(100% + 20vw);
position: relative;
left: -10vw;
}