themes-wordpress/seedlet/assets/sass/blocks/gallery/_style.scss

.wp-block-gallery {

	margin: 0 auto;

	.blocks-gallery-image,
	.blocks-gallery-item {

		figcaption {
			margin: 0;
			// Text color is always white to account for default gradient background
			color: var(--global--color-white);
			font: var(--global--font-size-sm);
		}
	}

	&.alignfull {
		.blocks-gallery-grid {
			width: 100%;
		}
	}
}