Depending on where you want to achieve it, you can try the creator kit. They already built a left navigation for canvas apps. Other than that as @Atmaram90 already mentioned CSS and HTML as custom css template, so that it can be taken for all pages at once.
For a first look how to format html and css you can have a look here: https://www.youtube.com/watch?v=0IZYHPjfMHo
you have to add custom css/html in web template or in page (editing in VS code) to achieve this
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