style.css

body{
    margin: 0;
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}
.pertambahan{
    border: solid 5px red;
    width: 100%;
    color: white;
    height: 50%;
    padding-left: 20px;
    background: darkkhaki;
    margin-top: 10px;
}
.perkalian{
    border: solid 5px green;
    width: 100%;
    color: white;
    height: 50%;
    padding-left: 20px;
    background:  darkolivegreen;
    margin-top: 20px;
}
.pembagian1{
    border: solid 5px yellow;
    width: 100%;
    height: 50%;
    padding-left: 20px;
    background: darkcyan;
    margin-top: 20px;
    color: white;
}
h1{
    text-align: center;
    color: navy;
}
button{
    background: yellow;
    color: black;
    border: solid 2px yellow;
    width: 150px;
    height: 40px;
}
button:hover{
    webkit-box-shadow: 0 8px 6px -6px black;
	   -moz-box-shadow: 0 8px 6px -6px black;
	        box-shadow: 0 8px 6px -6px black;
}
.input{
    width: 300px;
    height: 20px;
    border-radius: 30px;
    padding-left: 20px;
    color: blue;
}
label{
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    font-size: 20px;
}