If you want to create a button for a website using Illustrator, you can watch this video. First draw a 20-pixel rectangle. Now use a stroke and fill the inside with a nice gradient. You can use white and ash color to make a glossy button. Now, type inside the button using the type tool. Blue is good for typing. Though any kind of button can made by this, in the video an "Add to Cart" button is used as an example. By watching this video you can make Add to Cart and any other button using Illustrator.
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