:root {
    --bg-color: #0e0f14;
    --calculator-bg: #000;
    --bg-aux-btn: #CCC;
    --hover-bg-aux-btn: #000;
    --bg-opr-btn: #CD4631;
    --hover-bg-opr-btn: #FFF;
    --bg-num-btn: #686868;
    --hover-bg-num-btn: #FFF;
    --text-aux-btn: #000;
    --text-opr-btn: #FFF;
    --text-num-btn: #FFF;
    --text-area-text: #000;
}

* {
    margin: 0;
    padding: 0;
}

body {
    background-color: var(--bg-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-evenly;
}

main {
    display: flex;
    align-items: center;
    justify-content: center;
}

#calculator {
    width: 425px;
    height: 650px;
    display: flex;
    flex-direction: column;
    background-color: var(--calculator-bg);
    border-radius: 8px;
    box-shadow: 1px 2px 5px #FFF;
    padding: 1em;
    box-sizing: border-box;
}

#text-area {
    flex: 1;
    width: 100%;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    margin-bottom: 1em;
    border-top-left-radius: 5px;
    border-top-right-radius: 5px;
    transition: all 1s ease-in-out;
}

#button-area {
    display: flex;
    flex-direction: column;
    flex: 4;
}

#input,
#output {
    text-align: right;
    color: var(--text-area-text);
    padding: 0.2em 0.1em;
}

#input {
    font-size: 3em;
}

#output {
    font-size: 1.5em;
}

.button-row {
    box-sizing: border-box;
    justify-content: space-around;
    width: 100%;
    display: flex;
    flex: 1;
    margin-bottom: 0.5em;
}

.btn {
    display: flex;
    align-items: center;
    justify-content: center;
    flex: 1;
    border-radius: 50%;
    margin: 0.1em 0.2em;
    border: 1px solid transparent;
    font-size: 2em;
    transition: all 0.5s;
}

.btn:hover {
    position: relative;
    top: -0.1em;
    cursor: pointer;
}

.btn img {
    position: relative;
    left: -0.1em;
    width: 75%;
    height: 75%;
}

.aux-btn {
    background-color: var(--bg-aux-btn);
    color: var(--text-aux-btn);
}

.opr-btn {
    background-color: var(--bg-opr-btn);
    color: var(--text-opr-btn);
}

.opr-btn:hover {
    background-color: var(--hover-bg-opr-btn);
    color: var(--bg-opr-btn);
    border-color: var(--bg-opr-btn);
}

.num-btn {
    background-color: var(--bg-num-btn);
    color: var(--text-num-btn);
}

.num-btn:hover {
    background-color: var(--hover-bg-num-btn);
    color: var(--bg-num-btn);
    border-color: var(--bg-num-btn);
}

#power-btn {
    background-color: #2569bd;
    color: #FFF;
    border-color: #FFF;
}

#power-btn:hover {
    background-color: #094691;
    color: #CCC;
    border-color: #CCC;
}

footer {
    text-align: center;
    color: #FFF;
    background-color: var();
    font-weight: 100;
}

footer p:first-child {
    font-size: 1.4em;
    font-weight: 300;
}

footer a {
    text-decoration: none;
    color: #2569bd;
}

footer a:hover {
    color: #FFF;
}

/* Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) {
    #calculator {
        width: 350px;
        height: 600px;
    }

    #power-btn,
    .aux-btn,
    .opr-btn,
    .num-btn{
        height: 70px;
    }
}