style.css

@import url('https://fonts.googleapis.com/css?family=Montserrat');
*{
    margin:0;
    padding : 0;
    box-sizing: border-box;
}
html{
    font-size: 16px;
}
body{
    font-family : 'Montserrat',sans-serif;
    background-color : #505562;
    color : #fff;
}
.container{
    width : 500px;
    margin : 20px auto;
    user-select: none;
    overflow-x: hidden;
    position: relative;
}

.header {
    background-color: #2d2d37;
    text-align: center;
    padding: 1.75rem;
}
.header h1{
    font-size: 2.25rem;
}
.date{
    background-color: #222;
    text-align: right;
    font-size: 0.75rem;
    padding : 0.75rem 2rem 0.75rem 0;
}
ul.currencies{
    height : calc(100vh - 40px - 100px - 40px - 58px);
    background-color: #222;
    padding : 0 1.5rem 1rem 1.5rem;
    overflow-y: auto;
}
ul.currencies li{
    background-color : #2d2d37;
    border-radius: 5px;
    list-style: none;
    padding : 1rem 1rem 0.75rem 1rem;
    margin-bottom: 1rem;
    position: relative;
}
ul.currencies li:last-child{
    margin-bottom: 0;
}
ul.currencies li.base-currency{
    background-color : #264d73;
}
.flag{
    width : 60px;
    height : 40px;
    border : 1px solid #fff;
    vertical-align: top;
}
.info{
    display: inline-block;
    width: 78%;
}
.info .input span{
    font-size: 1.5rem;
    display: inline-block;
    width: 4rem;
    text-align : center;
}
.info .input input{
    font-size : 1.5rem;
    width: 78%;
    background-color: transparent;
    border: 2px solid #fff;
    border-radius: 5px;
    color : #fff;
    padding : 0.3rem;
    margin-bottom: 0.75rem;
}
.info .currency-name{
    font-size:1rem;
    font-weight : bold;
    margin-bottom: 0.5rem;
    margin-left : 4rem;
}
.info .base-currency-rate{
    font-size:0.8rem;
    margin-left : 4rem;
}
ul.currencies li .close{
    position: absolute;
    top : 0;
    right: 0;
    padding : 0 0.5rem ;
    font-size: 1.5rem;
    color : #666;
    cursor: pointer;
}
ul.currencies li .close:hover{
    color : #fff;
}
ul.currencies::-webkit-scrollbar{
    width : 5px;
}
ul.currencies::webkit-scrollbar-thumb{
    background-color : #2d2d37;
    border-bottom: 1rem solid #222;
}
ul.add-currency-list{
    position: absolute;
    bottom: 54px;
    left : 105%;
    background-color: #f1f1f1;
    color : #333;
    width:100%;
    height : calc(100vh - 40px - 100px - 55px);
    overflow-y: auto;
    transition: all 0.25s;
}
ul.add-currency-list li{
    list-style: none;
    padding : 0.375rem;
    border-bottom: 1px solid #ddd;
}
ul.add-currency-list li.disabled{
    opacity : 0.7;
    cursor: not-allowed;
}
ul.add-currency-list li .flag{
    width:3rem;
    height: 2rem;
    vertical-align: middle;
}
ul.add-currency-list li span{
    margin-left: 1rem;
    font-weight: bold;
}
.add-currency-btn{
    background-color : #00b386;
    color : #fff;
    padding : 1rem;
    font-size: 1.2rem;
    font-weight: bold;
    border: none;
    border-top: 3px solid #222;
    outline : none;
    width : 100%;
    cursor : pointer;
    transition : background-color 0.25s;
    position: relative;
}
.add-currency-btn i{
    position: absolute;
    top : 0.6rem;
    left : 30%;
    font-size: 2rem;
    opacity: 0;
    transition: all 0.25s;
}

.add-currency-btn.open{
    background-color: #d9534f;
}
.add-currency-btn.open i{
    opacity: 1;
    left : 1.25rem;
}
.add-currency-btn.open  + ul.add-currency-list{
    left : 0;
}
.add-currency-btn.open  + ul.add-currency-list li:hover{
    background-color: #ddd;   
}
@media (max-width : 600px){
    html{
    font-size:14px;
    }
    .container{
        width : 100%;
        margin : 0 auto;
    }
    ul.currencies{
        height : calc(100vh - 83px - 34px - 51px);
    }
    .header h1{
        font-size : 2rem;
    }
    .flag{
        width : 3rem;
        height:2rem;
    }
    .info .input span{
        font-size: 1.25rem;
        width : 3.5rem;
    }
    .info .input input{
        font-size: 1.25rem;
        width:76%;
    }
    .info .currency-name{
        margin-left :3.5rem;
    }
    .info .base-currency-rate{
        margin-left : 3.5rem;
    }
    ul.add-currency-list{
        bottom : 48px;
        height:calc(100vh - 80px - 51px);
    }
    
    .add-currency-btn i {
        left:25%;
        top : 0.65rem;
    }
}