After completing the setup of your html css and js project you will now have to insert some front end code to build your calculator. Below is a html code that you have to copy and paste in your index.html file.
<button>7</button>
<button>8</button>
<button>9</button>
<button>+</button>
<button>4</button>
<button>5</button>
<button>6</button>
<button>-</button>
<button>1</button>
<button>2</button>
<button>3</button>
<button>*</button>
<button>0</button>
<button>C</button>
<button>=</button>
<button>/</button>