Material Design.

App inventor does not have the tools to create a standard "material design".

Is there an easy way to change this?

How to remove the top title bar of the application feature to be directed?

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The answer to your first question is here:  http://appinventor.mit.edu/appinventor-sources/

The answer to your second question has been discussed many times and you can not do it with standard app inventor.  You could  search in the forum using the Search for topics box to the right of the colorful google at the top of this page  using a term like title bar    or title bar remove.

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you can remove the title bar with AppToMarket

Advice: Before posting, it's a good idea to search in this forum. Many others have likely run into problems similar to yours. How to search see screenshot.

See also the  Top 5 Tips: How to learn App Inventor

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Can I remove the title bar without AppToMarket?

I made the program I put several times in google play and now when I remove the bar with AppToMarket the program is not accepted by google play.

What can I do wrong?

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No... presently, in AI2, there's no way to remove the title bar.

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