The whole decscription is given below
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the index file contains the buttons to input all operators.

It is divided into two sections.
i. calculator
ii. results

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the style folder contains its styling  in "app.css" file.
the "index.html" different sections are beautified by this css file.
I've used different styling properties eg. padding,shadow,different colours,etc...

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the script folder contains two files
i. vendor.js
      here i've declared different variables to store data in it and display the output result.

ii. script.js
            this file contains the different functions to perform operations and to return the result and its description.

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PS: I've used Visual Studio Code to write this code.
    I've taken support of W3School website for some issues.