*{
margin: 0;
padding: 0;
box-sizing: border-box;

font: bold 14px Arial, sans-serif;
}

html {
height: 100%;
background: white;
background-size: cover;
}

#calculator {
width: 325px;
height: auto;
margin: 100px auto;
padding: 20px 20px 9px;
background: #bce6ba;
background: linear-gradient(#bce6ba,#f1f8ba );
border-radius: 6px;
box-shadow: 0px 4px #bed7a5, 0px 10px 15px rgba(0, 0, 0, 0.2);
}

.top span.clear {
float: left;
}
.top .screen {
height: 40px;
width: 212px;
float: right;
padding: 0 10px;
background: rgba(0, 0, 0, 0.2);
border-radius: 3px;
box-shadow: inset 0px 4px rgba(0, 0, 0, 0.2);
font-size: 17px;
line-height: 40px;
color: white;
text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.2);
text-align: right;
letter-spacing: 1px;
}

.keys, .top {overflow: hidden;}

.keys span, .top span.clear {
float: left;
position: relative;
top: 0;
cursor: pointer;
width: 66px;
height: 36px;
background: white;
border-radius: 3px;
box-shadow: 0px 4px rgba(0, 0, 0, 0.2);
margin: 0 7px 11px 0;
color: #888;
line-height: 36px;
text-align: center;
user-select: none;
/*css3*/
transition: all 0.2s ease;
}

.keys span.operator {
background: #FFF0F5;
margin-right: 0;
}
.keys span.equal {
background: #f0f0a0;
box-shadow: 0px 4px #9da853;
color: #888e5f;
}
.top span.clear {
background: #ff9fa8;
box-shadow: 0px 4px #ff7c87;
color: white;
}

.keys span:hover {
background: #64a08c;
box-shadow: 0px 4px #3c7878;
color: white;
}
.keys span.equal:hover {
background: #abb850;
box-shadow: 0px 4px #717a33;
color: #ffffff;
}
.top span.clear:hover {
background: #f68991;
box-shadow: 0px 4px #d3545d;
color: white;
}
.keys span:active {
box-shadow: 0px 0px #6b54d3;
top: 4px;
}
.keys span.equal:active {
box-shadow: 0px 0px #717a33;
top: 4px;
}
.top span.clear:active {
top: 4px;
box-shadow: 0px 0px #d3545d;
}
