* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: sans-serif;
}

.app {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator {
    background-color: #22252D;
    width: 100%;
    max-width: 375px ;
    min-height: 640px;
    display: flex;
    flex-direction: column;
    border-radius: 1.5rem;
    overflow: hidden;
}

.display {
    min-height: 200px;
    padding: 1.5rem;
    display: flex;
    justify-content: flex-end;
    align-items: flex-end;
    color: white;
    text-align: right;
    flex: 1 1 0%;
}

.display .content {
    display: flex;
	flex-direction: column;
	justify-content: flex-end;
	width: 100%;
	max-width: 100%;
	overflow: auto;
}

.display .input {
    font-size: 1.25rem;
    width: 100%;
    margin-bottom: 0.5rem;
}


.display .output {
    font-size: 3rem;
    font-weight: 700;

    white-space: nowrap;
    width: 100%;
}

.display .operator {
    color: red
}

.display .operator, 
.display .percent {
    color: rgb(255, 0, 0);
}

.keys { 
    background-color: #292D36;
    padding: 1.5rem;
    border-radius: 1.5rem 1.5rem 0 0;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(5, 1fr);
    grid-gap: 1rem;
    box-shadow: 0px -2px 16px rgba(0,0,0,0.2);
}

.keys .key {
    position: relative;
    cursor: pointer;
    background-color: #323742;
    display: block;
    height: 0;
    padding-top: 100%;
    transition: 0.2s;
    user-select: none;
}

.keys .key span {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 2rem;
    font-weight: 700;
    color: white;
}

.keys .key:hover {
    box-shadow: inset 0px 0px rgba(0,0,0,0.2);
    background-color: grey;
}

.keys .key.operator span {
    color: red;
}

.keys .key.action  span{
    color: turquoise;
}