style.css

html {
	min-height: 100%;
    }

body {
    background: #464646; /* For browsers that do not support gradients */
    background: -webkit-linear-gradient(#000000, #464646); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(#000000, #464646); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(#000000, #464646); /* For Firefox 3.6 to 15 */
    background: linear-gradient(#000000, #464646); /* Standard syntax (must be last) */
    font-family: 'Open Sans', sans-serif;
}

#container {
    height: 718px;
    width: 600px;
    background-color: #5a7775;
    margin: 150px auto;
}

#calculation {    
    width: 100%;
    background-color: #bcd5d4;
    height: 50px;
    margin-bottom: 0px;
}

#calculation p {
    color: #393939;
    font-size: 35px;
    text-align: right;
    padding-right: 25px;
    line-height: 50px;
}

#answer {
    width: 100%;
    background-color: #bcd5d4;
    height: 100px;
    margin-top: 10px;
}

#answer p {
    color: #393939;
    font-size: 35px;
    text-align: right;
    padding-right: 25px;
    line-height: 100px;
}

#row1 {
    margin-top:25px;
}

#col1 {
    height: 100px;
    width: 24%;
    background-color: #3f615f;
    margin-right: 7.7px;    
    margin-bottom: 2px;
    float: left;
}

#col1 p {
    color: #b9b9b9;
    text-align: center;
    font-size: 35px;
    line-height: 30px;
}

#col2 {
    height: 100px;
    width: 24%;
    background-color: #3f615f;
    margin-right: 7.7px;    
    margin-bottom: 2px;
    float: left;
}

#col2 p {
    color: #b9b9b9;
    text-align: center;
    font-size: 35px;
    line-height: 30px;
}

#col3 {
    height: 100px;
    width: 24%;
    background-color: #3f615f;
    margin-right: 7.7px;    
    margin-bottom: 2px;
    float: left;
}

#col3 p {
    color: #b9b9b9;
    text-align: center;
    font-size: 35px;
    line-height: 30px;
}

#col4 {
    height: 100px;
    width: 24%;
    background-color: #3f615f;    
    margin-bottom: 2px;
    float: right;
}

#col4 p {
    color: #b9b9b9;
    text-align: center;
    font-size: 35px;
    line-height: 30px;
}