In Writer for Windows, you have different options to change the rendering of Preview: the fonts, the layout or even background color.
You can choose between Web mode (rendering HTML) or PDF mode: simply toggle ON and OFF the PDF mode on the top right of the Toolbar.
You have more formatting options available in PDF mode via Preferences → Templates.
If you make changes to your document, you can click the refresh button at the bottom right of the PDF preview to see these changes reflected.
In the Web mode, you can invert the colors to mark the difference between the Editor and Preview.
By default, Preview will scroll in parallel with the Editor. If you wish to scroll the panes independently, you can disable the parallel scrolling in File → Preferences → Editor → Synchronize Scroll.
You can modify the font and layout of the document in the Preview thanks to the Templates:
Preview determines what Export will look like. In the case of PDF, the currently selected typography in the Preview will be used.
If you are familiar with web development, you surely know the inspector tool lets you see parts of the code rendered by the page, such as HTML and CSS. You can enable the Web Inspector tool in the Preview, in case you wanted to know what your document is like, under the hood.
On Windows, you can enable the Chromium inspector by using Ctrl J.
Modify the Preview 
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In Writer for iOS, you have different options to change the rendering of Preview: the fonts, layout or even background color. Web & PDF Modes You can choose between Web or PDF view. You have more formatting options available for PDF via Settings → Templates. In the Web view, you can invert the colors to
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iA Writer for Android comes with a couple of in-app templates rendering in Preview. Preview determines what Export will look like. You can change the rendering of Preview by switching Templates. The ”template” button let you change the currently selected template. Thanks to those templates, you can modify the font and layout of the rendered
In Writer for Windows, you have different options to change the rendering of Preview: the fonts, the layout or even background color. Web & PDF Modes You can choose between Web mode (rendering HTML) or PDF mode: simply toggle ON and OFF the PDF mode on the top right of the Toolbar. You have more