zotero/scss/elements/_attachmentPreview.scss

attachment-preview {
	width: 100%;
	padding: 0px;
	display: flex;
	flex-direction: column;
	align-items: center;
	transition: height 0.2s ease-in-out, opacity 0.2s ease-in-out;
	// This is set in JS
	// Suppose it's A4 size
	--width-height-ratio: 0.7070707071;
	--min-height: 56px;
	--max-height: 600px;
	// This is set in JS
	--preview-width: 400;
	--preview-height: calc(min(var(--preview-width) / var(--width-height-ratio), var(--max-height)));
	max-height: var(--max-height);

	&[hidden] {
		display: none;
	}

	#preview {
		display: inline-block;
		width: 100%;
		height: 100%;
		// Make sure minimal height before loading
		min-height: var(--preview-height);
		border-radius: 5px;
		border: var(--material-border-quarternary);
		pointer-events: none;
	}

	#next-preview {
		display: none;
	}

	.icon {
		// Force the image to load, otherwise the first dragging will not show a drag image
		display: inline-block;
		opacity: 0;
		width: 100%;
		height: 1px;
		max-height: 1px;
		margin-bottom: -1px;
	}

	$preview-icons: (
		file: "document",
		pdf: "attachment-pdf",
		snapshot: "attachment-snapshot",
		epub: "attachment-epub",
	);

	@each $cls, $icon in $preview-icons {
		&[data-preview-type="#{$cls}"] {
			.icon {
				@include focus-states using ($color) {
					@include svgicon($icon, $color, "28", "item-type");
				}
			}
		}
	}

	.btn-container {
		display: flex;
		justify-content: center;
		gap: 6px;
		position: relative;
		margin-top: -28px;
		bottom: 6px;

		toolbarbutton {
			padding: 4px;
			background-color: rgba(0,0,0,0.5);
			
			&:hover {
				background-color: rgba(0,0,0,0.4);
			}

			&:active, &[selected] {
				background-color: rgba(0,0,0,0.3);
			}

			&:disabled,
			&[disabled="true"] {
				background-color: rgba(0,0,0,0.2);
			}
		}
	}

	.btn-prev {
		@include svgicon-menu("arrow-left", "universal", "20", false, false, (#fff, #fff));
	}

	.btn-next {
		@include svgicon-menu("arrow-right", "universal", "20", false, false, (#fff, #fff));
	}

	.drag-container {
		width: 64px;
		height: 64px;
		position: absolute;
		top: -10000px;

		.icon {
			opacity: 1;
			height: 56px;
			max-height: 56px;
			margin-bottom: 0px;
		}
	}

	&[data-preview-type=pdf] {
		#preview {
			border: 0;
		}

		.btn-container {
			// PDF page has 3px vertical padding so we offset 6px more
			bottom: 12px;
		}
	}

	&[data-preview-type=snapshot] {
		#preview {
			pointer-events: all;
		}

		.btn-container {
			display: none;
		}
	}

	$other-preview-types: (
		image,
		video,
		audio,
	);

	@each $cls in $other-preview-types {
		##{$cls}-preview {
			display: none;
			width: 100%;
			height: 100%;
			object-fit: contain;
			border-radius: 5px;
			border: var(--material-border-quarternary);
			max-height: var(--preview-height);
			min-height: var(--min-height);
			max-width: calc((var(--preview-height) - 2px) * var(--width-height-ratio));
		}

		&[data-preview-type="#{$cls}"] {
			#preview {
				display: none;
			}

			.btn-container {
				display: none;
			}

			##{$cls}-preview {
				display: inline-block;
			}
		}
	}

	&:not(:hover) {
		.btn-container {
			display: none;
		}
	}

	&[data-preview-status=fail] {
		#preview {
			display: none;
		}

		.icon {
			display: inline-block;
			opacity: 1;
			height: 56px;
			max-height: 56px;
			margin-bottom: 0px;
		}

		.btn-container {
			display: none;
		}
	}

	&[data-preview-status=loading] {
		opacity: 0;
		#preview {
			opacity: 0;
		}
	}
}