1. You can add placeholders in your code – edit this line:
<input type="text" value="' . get_search_query() . '" name="s" id="s" />
to:
<input type="text" value="' . get_search_query() . '" name="s" id="s" placeholder="Your placeholder text here" />
2. Try this CSS to style search field background:
.toolzview_sarchbox input[type=text] {
background-color: rgbas(255,255,255,0.5);
min-width: 220px; /* Set minimumn width to cover mobile */
width: 50%; /* Set width for all devices */
margin-right: -5px; /* Remove margin between inputs */
}