main.css

:root {
    --primary-color:#5fbaa7;
}

*{
    box-sizing:border-box;
}

body {
    background-color: #f4f4f4;
    font-family: Arial, Helvetica, sans-serif;
    display:flex; /* automatically align everything horizontally */
    flex-direction: column; /* put the above back */
    align-items:center; /* align horizontally  */
    justify-content: center; /* line it vertically */
    height:100vh;
    margin:0;
    padding:20px;
}

h1 {
    color:var(--primary-color);
}

p {
    text-align:center;
}

.btn {
    color:#fff;
    background:var(--primary-color);
    cursor:pointer;
    border-radius:5px;
    font-size:12px;
    padding:5px 12px;
}

.money-img {
    width:150px;
}

.currency {
    padding:40px 0;
    display:flex;
    align-items:center;
    justify-content: space-between; /*which will take the remaining space and put it between */
}

.currency select {
    padding:10px 20px 10px 10px;
    -moz-appearance: none;
    -webkit-appearance: none;
    appearance: none;
    border:1px solid #dedede;
    font-size:16px;
    background: transparent;
    background-image:url('data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%22292.4%22%20height%3D%22292.4%22%3E%3Cpath%20fill%3D%22%20000002%22%20d%3D%22M287%2069.4a17.6%2017.6%200%200%200-13-5.4H18.4c-5%200-9.3%201.8-12.9%205.4A17.6%2017.6%200%200%200%200%2082.2c0%205%201.8%209.3%205.4%2012.9l128%20127.9c3.6%203.6%207.8%205.4%2012.8%205.4s9.2-1.8%2012.8-5.4L287%2095c3.5-3.5%205.4-7.8%205.4-12.8%200-5-1.9-9.2-5.5-12.8z%22%2F%3E%3C%2Fsvg%3E');
    background-position:right 10px top 50%, 0, 0;
    background-size:12px auto, 100%;
    background-repeat:no-repeat;
}

.currency input {
    border:0;
    background: transparent;
    font-size:30px;
    text-align:right;
}

.swap-rate-container {
    display:flex;
    align-items:center;
    justify-content:space-between;
}

.rate {
    color:var(--primary-color);
    font-size:14px;
    padding:0 10px;
}

select:focus,
input:focus,
button:focus {
    outline:0;
}

@media (max-width:600px){
    .currency input {
        width:200px;
    }
}