body{font-family: "A1 Gothic R";}

@media (min-width: 641px) {
    #index_nav a {
        padding: 10px 0;
        display: block;
        transition: opacity .1s ease;
    }
}

@media (max-width: 640px) {
    #index_nav .date {
        font-size: 10px;
        letter-spacing: .1em;
        color: #666;
    }
}

@media (max-width: 640px) {
    #index_nav a {
        padding: calc(30 / 640* 100vw) 0;
        display: block;
        transition: opacity .1s ease;
    }
}

@media (min-width: 641px) {
    #index_nav .date {
        font-size: 11px;
        letter-spacing: .1em;
        color: #666;
    }
}