body, ul{
    margin: 0;
}

header{
    border-bottom: 1px solid #d7d7d7;
    background: #fbfbfb;
}

.navigation{
    display: flex;
    align-items: center;
    list-style: none;
    height: 80px;
}

.navigation li{
    margin-left: 1em;
    cursor: pointer;
}

.navigation .current{
    font-weight: bold;
}

iframe{
    width: 100%;
    height: calc(100vh - 80px);
    border: none;
}