index.css

html, body {
    margin: 0;
    padding: 0;
    font-family: Verdana, sans-serif;
    font-size: 20px;
    background-color: hsl(0, 0%, 93%);
    height: 100%;
    overflow: scroll;
}

body > main {
    width: 500px;
    margin: 20px auto;
}

body > main > h1 {
    text-align: center;
}

a {
    text-decoration: none;
}

input[type=text], input[type=tel] {
    display: block;
    width: 100%;
    box-sizing: border-box;
}

div.form-field {
    margin-bottom: 10px;
}

div#call-button {
    margin-top: 50px;
    text-align: center;
}

span#connect {
    position: relative;
}

cvg-webrtc-button > svg {
    display: block;
    height: 25px;
}

cvg-webrtc-button::part(trigger) {
    border: 0;
    color: hsl(0, 0%, 80%);
    fill: hsl(0, 0%, 80%);
    background-color: hsl(120, 100%, 15%);
    padding: 10px 20px;
    border-radius: 4px;
}
cvg-webrtc-button::part(trigger-enabled):hover {
    background-color: hsl(120, 100%, 30%);
}
cvg-webrtc-button::part(trigger-enabled):active {
    color: hsl(0, 0%, 100%);
    fill: hsl(0, 0%, 100%);
}
cvg-webrtc-button::part(trigger-disabled) {
    background-color: hsl(0, 100%, 20%);
    text-decoration: line-through;
}