index.css

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

body {
    background-color: #000;
}

.main {
    width: 100%;
    display: flex;
    align-items: flex-end; 
    justify-content: center;
    padding: 1rem;
    position: relative; 
    height: 100vh; 
}

canvas {
    width: 100%; 
    height: 100%; 
    box-shadow: 0 0 4px 1px #fff;
}

.upload_audio {
    padding: 1rem;
    background-color: #000;
    color: #fff;
    font-size: 2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    position: absolute; 
    top: 30px;
    left: 50%; 
    transform: translateX(-50%); 
}

@media(max-width:490px) {
    .upload_audio {
        font-size: 1rem;
    }
}

.upload_audio i {
    margin-left: 0.5rem;
}

input {
    position: absolute;
    top: 0;
    left: 0;
    opacity: 0;
    width: 100%;
    height: 100%;
    cursor: pointer;
}