To center an image in a Steemit post, put your image inside the 'center' coding shown below in the example. The image ends up looking like this:

To center an image in a Steemit post, simply type this 'center' coding in your post. But, where it says image.png place your image URL there or upload your image there directly in Steemit by clicking the blue link under your post editing area that says 'select your image'... and make sure you have it between the center coding like the example.

To center some text in a Steemit post, do the same thing, but replace the image file with you text.. just like this:

...and it will end up looking like this:
I hope this was helpful for you. If it was, please upvote this post, comment any questions you still have, and follow me @mitchmahoney around the world.
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credit: @kkugel2 ?
Thank you very much man! I did it finally with simple code..