:root {
    --digit-keys: #505050;
    --operator-keys: #FF9500;
    --background-color: #1C1C1C;
    --function-keys: #a2a2a2;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    user-select: none;
    font-family: Helvetica, sans-serif;
}

body { 
    background-color: var(--background-color);
    color: #ffffff;
    height: 100%;
    width: 100%;
}

a, a:visited {
    color: #ffffff;
}

li {
    list-style: none;
}

span {
    font-weight: bold;
}

hr {
    margin: 0;
    align-self: stretch;
}

/* Made By SAJID :) */

.col:first-child {
    order: 2;
}

.calculator {
    display: flex;
    flex-direction: column;
    min-height: 500px;
    min-width: 290px;
    font-size: 1.3rem;
}

.main-content {
    display: flex;
    flex-direction: column;
    padding: 0 3rem 0 3rem;
}

.main-content main, .main-content section {
    padding: 1rem 0 1rem;
    width: 100%;
}

.main-content header, .main-content section h2 {
    padding-bottom: 1rem;
    width: 100%;
}


.calculator .screen {
    display: flex;
    justify-content: end;
    align-items: flex-end;
    padding: 0 0 15px 0;
    font-size: 5.5rem;
    width: 290px;
    height: 150px;
    overflow-x: hidden;
}

.calculator .keyboard {
    width: 290px;
    height: 350px;
}

/* applying background colors */

/* first row by sajid */
.keyboard .row:first-child .sub-col:not(:last-child) {
    background-color: var(--function-keys);
    color: var(--background-color);
}

.keyboard .row:first-child .sub-col:last-child {
    background-color: var(--operator-keys);
    color: #ffffff;
}

/* second row, third row, fourth row and fifth row */
.keyboard .row:nth-child(2) .sub-col:not(:last-child), 
.keyboard .row:nth-child(3) .sub-col:not(:last-child), 
.keyboard .row:nth-child(4) .sub-col:not(:last-child), 
.keyboard .row:nth-child(5) .sub-col:not(:last-child) {
    background-color: var(--digit-keys);
    color: #ffffff;
}

.keyboard .row:nth-child(2) .sub-col:last-child, 
.keyboard .row:nth-child(3) .sub-col:last-child, 
.keyboard .row:nth-child(4) .sub-col:last-child, 
.keyboard .row:nth-child(5) .sub-col:last-child {
    background-color: var(--operator-keys);
    color: #ffffff;
}

.selected_operation[data-value='clear'], 
.selected_operation[data-value='%'], 
.selected_operation[data-value='+/-'] {
    animation: background-anim-fn .8s ease-out;
}

.selected_operation[data-value='='] {
    animation: background-anim-equals .8s ease-out;
}

/* Select every operator button except clear, %, +/- and = */
.selected_operation[data-button-type='operator']:not(.selected_operation[data-value='clear']):not(.selected_operation[data-value='%']):not(.selected_operation[data-value='+/-']):not(.selected_operation[data-value='=']) {
    background-color: #d4d4d2;
    color: var(--operator-keys);   
    transition: background-color, color .8s ease-out;
}

@keyframes background-anim-fn { 
    0% { background-color: var(--function-keys); }
    50% { background-color: #fff;  }
    100% { background-color: var(--function-keys); }
}

@keyframes background-anim-equals {
    0% { background-color: var(--operator-keys); }
    50% { background-color: #fff;  }
    100% { background-color: var(--operator-keys); }
}
/* utilities */

.row {
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    -ms-flex-wrap: wrap;
    flex-wrap: wrap;
}

.col { 
    display: flex;
    position: relative;
    width: 100%;
    -webkit-box-flex: 0;
    -ms-flex: 0 0 100%;
    flex: 0 0 100%;
    max-width: 100%;
    height: 100vh;
}

@media only screen and (min-width: 992px) {
    .col { 
        -ms-flex: 0 0 50%;
        flex: 0 0 50%;
        max-width: 50%;
    }
}

.flex-center {
    justify-content: center;
    align-items: center;
}

.sub-col {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 21%;
    height: 86%;
    -webkit-box-flex: 0;
    -ms-flex: 0 0 21%;
    flex: 0 0 21%;
    max-width: 21%;
    border-radius: 50%;
    transition: background-color .8s ease-out;
}

.row:last-child > .sub-col:first-child {
    display: flex;
    justify-content: start;
    padding-left: 25px;
    width: 47%;
    -ms-flex: 0 0 47%;
    flex: 0 0 47%;
    max-width: 47%;
    border-radius: 100px 100px 100px 100px;
    transition: background-color .8s ease-out;
}

.keyboard .row {
    justify-content: space-between;
    height: 20%;
}

/* responsive settings by sajid */

@media only screen and (min-width: 992px) {
    .col:first-child {
        order: 0;
    }

    .main-content {
        display: flex;
        justify-content: center;
        align-items: center;
        padding: 0;
        max-width: 350px;
    }
}

@media only screen and (min-width: 1500px) {
    .main-content {
        font-size: 1.4rem;
        max-width: 450px
    }

    .calculator {
        min-height: calc(500px / .7);
        min-width: calc(290px / .7);
        font-size: 1.7rem;
    }

    .calculator .screen {
        display: flex;
        justify-content: end;
        align-items: flex-end;
        padding: 0 0 15px 0;
        font-size: 7rem;
        width: calc(290px / .7);
        height: calc(150px / .7);
        overflow-x: hidden;
    }
    
    .calculator .keyboard {
        width: calc(290px / .7);
        height: calc(350px / .7);
    }

}