popup.css

body {
    background: #f1f1f1;
    font-family: Verdana, Helvetica, Arial, sans-serif;
    font-size: 16px;
    height: 320px;
    width: 320px;
    margin: 0;
    overflow: hidden;
    box-shadow: 0 2px 4px 0 rgba(0, 0, 0, 0.16), 0 2px 10px 0 rgba(0, 0, 0, 0.12);
}

.header {
    align-items: center;
    background: #fff;
    height: 64px;
    display: flex;
}

.header-link {
    color: #d20505;
    font-weight: bold;
    line-height: 20px;
    text-decoration: none;
    margin: 0px auto;
}

.header-link:focus {
    outline: none;
}

.header-logo {
    display: inline-block;
    width: 50px;
    margin-right: 10px;
    position: relative;
    top: 15px;
}

.header-text {
    display: inline-block;
}

.container {
    overflow-y: auto;
    padding: 16px 24px 0px 24px;
    text-align: center;
    height: 240px;
    align-items: center;
    justify-content: center;
}

.container button {
    cursor: pointer;
    width: 150px;
    height: 40px;
    border: none;
    border-radius: 12px;
    font-size: 15px;
    color: #fff;
    background: #d20505;
    box-shadow: 0 3px #ab3c3c;
    font-family: inherit;
    font-weight: 700;
    outline: none;
    margin-top: 30px;
}

span#youtubeURL {
    font-size: 12px;
    color: #333;
    display: block;
}

button#repeatYoutube:disabled {
    background: #ef6a6a;
    box-shadow: 0 3px #ab3c3c;
    cursor: not-allowed;
}

button#stopYoutube {
    margin: 30px auto;
}

button#repeatYoutube {
    margin: 30px auto;
}