I'm trying to style a select input on iOS. The first option or initial state should have smaller font-size but not the rest of the options.

I have the following html structure:

<select class="dropdown">
    <option selected="" value="Navigation">Navigation</option>
    <option value="some-link">Whatever</option>
    <option value="some-link">Another option</option>
    <option value="some-link">Why</option>
    <option value="some-link">What</option>
</select>

My CSS for it looks like this:

select {
    -webkit-appearance: none;
    font-family: 'Custom-Font', sans-serif;
    font-size:.5em
    line-height:1.8em; // optical center
    background-color: #ccc;
    color: #333;
    border: none;
    padding: 6px 10px 4px 10px;
}

.dropdown {
    background-image: url(img/assets.svg);
    background-position: right 2px;
    background-repeat: no-repeat;
    width: 100%;
    display:block;
    margin-bottom:-1.5em;

    option:not(:first-of-type) {
        font-size:1.5em;
    }
}

The <select> menu looks exactly like I want it to look. It says "Navigation" inside a light-gray box with a rather small font-size.

However when clicking/tapping the select on my iphone the native UI view of iOS shows all options also in a very small font-size.

How can I just make the selected option (or the box itself) use the custom formatting but not the options. I want my options to have a "normal" readable font-size.

Any ideas on that? I tried with option:not(:first-of-type) and increase the font-size but no effect!