<!DOCTYPE html>
<style>
    ::selection { background-color: rgba(63, 128, 33, 0.95); color: yellow; }
</style>
<input id="inputText" type="text" value="Hello" style="border: 5px solid;
    width:100px; font-size: 16px; font-family:sans-serif;
    padding: 0; margin: 0; outline:none;"><br>
<br>The above selected text in the input box should have green background and yellow color.
<script>
    window.onload = document.getElementById('inputText').select();
</script>