woocommerce/plugins/woocommerce-admin/client/customize-store/assembler-hub/sidebar/sidebar-navigation-screen-homepage/style.scss

.woocommerce-customize-store__sidebar-homepage-content {
	.block-editor-block-patterns-list__item {
		.auto-block-preview__container,
		.block-editor-block-preview__container {
			border: none;
		}

		&.is-selected {
			.auto-block-preview__container,
			.block-editor-block-preview__container {
				box-shadow: 0 0 0 0 #fff,
					0 0 0 2px var(--wp-admin-theme-color, #3858e9);
				border-color: var(--wp-admin-theme-color);
				border-radius: 4px;
				&::after {
					outline: none;
				}
			}
		}

		&:hover {
			.auto-block-preview__container,
			.block-editor-block-preview__container {
				box-shadow: 0 0 0 0 #fff,
					0 0 0 2px var(--wp-admin-theme-color, #3858e9);
				border-color: var(--wp-admin-theme-color);
				border-radius: 4px;
				&::after {
					outline: none;
				}
			}
		}
	}
}