html {
    -webkit-text-size-adjust: 100%;
}

* {
    box-sizing: border-box;
}

body {
    overflow-wrap: anywhere;
}

button,
input,
select,
textarea {
    font: inherit;
}

button,
input[type="number"] {
    min-height: 44px;
}

@media (max-width: 640px) {

    header {
        padding: 12px;
    }

    .header-inner {
        display: block;
    }

    .brand {
        display: block;
        margin-bottom: 14px;
    }

    nav {
        display: grid;
        grid-template-columns: 1fr 1fr 1fr;
        gap: 8px;
    }

    nav a {
        text-align: center;
        padding: 10px 5px;
        border: 1px solid #ddd;
        border-radius: 8px;
    }

    main {
        margin-top: 16px;
        padding-left: 12px;
        padding-right: 12px;
    }

    .grid {
        grid-template-columns: 1fr;
    }

    .product,
    .detail,
    .intro {
        padding: 16px;
    }

    form[action="/cart/add"] {
        display: grid;
        gap: 12px;
    }

    form[action="/cart/add"] input[type="number"] {
        width: 100%;
    }

    form[action="/cart/add"] button {
        width: 100%;
    }
}