You need to override your CSS so that you can change the background to black. An easy way to do this is to create a custom css class (you can put it in the <style type="text/css"> in your HTML or put it in a separate CSS file)
.black-background {background-color:#000000;} .white {color:#ffffff;}
Then give your button these classes
<input type="submit" class="btn btn-primary black-background white" value="Text" />
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