main.css

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    font-family: 'Montserrat', sans-serif;
    background-color: #29303B;
}

.wrapper {
    padding: 50px;
    width: 800px;
    background-image: linear-gradient(#3F4B59, #333D46);
    color: #fff;
    text-align: center;
    border: 1px solid #1C232D;
    border-radius: 15px;
    box-shadow: 0 0 15px #1C232D;
}

.wrapper h1 {
    margin-bottom: 10px;
    font-size: 36px;
}

.wrapper p {
    margin-bottom: 50px;
    font-size: 26px;
    font-weight: 200;
}

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

.section-left, .section-right {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.app-body input {
    margin-bottom: 10px;
    width: 100%;
    font-size: 60px;
}

.app-body input, .app-body select {
    color: #fff;
    border: none;
    background: none;
    text-align: center;
}

.app-body select {
    padding: 10px 20px;
    font-size: 36px;
    cursor: pointer;
}

.app-body input:focus, .app-body select:focus {
    outline: none;
    color: rgb(67,171,255);
}

.app-body option {
    color: #333;
}

.swap {
    align-self: flex-end;
    margin: 5px;
    padding: 5px 50px;
    background-image: linear-gradient(45deg, #2b89e7, #11e763);
    font-size: 30px;
    border: none;
    border-radius: 25px;
    color: #fff;
    cursor: pointer;
}

.swap:focus {
    outline: none;
    background-image: linear-gradient(45deg, #317fcc, #1fc06a);
}

.wrapper .rate-info {
    margin-top: 30px;
    margin-bottom: 0;
}