The text color of the widget can be customized, as well as the color and the alpha of the background. Press the result or formula in the widget to open the app.
<ahref='https://play.google.com/store/apps/details?id=com.simplemobiletools.calculator'><imgsrc='https://simplemobiletools.com/images/button-google-play.svg'alt='Get it on Google Play'height=45/></a>
<ahref='https://f-droid.org/packages/com.simplemobiletools.calculator'><imgsrc='https://simplemobiletools.com/images/button-f-droid.png'alt='Get it on F-Droid'height=45></a>