<!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>Fix for ::selection pseudo element to work on input elements.
<br>The above selected text in the input box should have green background and yellow color.
<script>
    document.getElementById('inputText').select();
</script>