Hi Rebecca,
Try adding my-grid
to the class list of the Grid Block as such: https://share.getcloudapp.com/5zurBeRd
Then, add this custom CSS in Appearance > Customize > Additional CSS:
.my-grid > .gb-grid-column > .gb-container > .gb-inside-container {
display: flex;
flex-direction: column;
height:100%;
}
.my-grid > .gb-grid-column > .gb-container > .gb-inside-container .wp-block-buttons {
margin-top:auto;
}
Kindly let us know how it goes.