.panel {
    width: 320px;
    margin: 20px auto;
    border: 1px solid rgba(255, 255, 255, 0.5);
    background-color: rgba(0, 0, 0, 0.75);
    border-radius: 20px;
    padding: 16px;
    text-align: center;
}

.panel.panel-sm {
    width: 260px;
}

.panel.panel-md {
    width: 320px;
}

.panel.panel-lg {
    width: 600px;
}

.panel div {
    margin: 0;
    padding: 0;
}

.panel button {
    display: block;
    width: 100%;
    text-transform: capitalize;
    font-size: 1.1em;
}

.panel .btn-group {
    width: auto;
    margin: 0 auto;
}

.panel .btn-group button {
    width: auto;
}

/* screen specific */

@media (max-width: 600px) {
    .panel.panel-lg {
        width: 100%;
    }
}