index.html

<!DOCTYPE html>
<html lang="ru">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width">
	<meta charset="utf-8">
    <title>Online-Stores</title>
    <link rel="stylesheet" href="styles.css">
	<meta name="format-detection" content="telephone=no">
	<meta name="description" content="">
	<meta name="kewords" content="">
	<link rel="shortcut icon" href="logo_vkladka.gif">
</head>
<body> 

    <header>
        <div class="header_container">
                <img class="header_container-logo" height="75px" src="os2.svg" alt="Logo">
             <div class="header_input">
        <input type="text" placeholder="      Поиск" class="header_search">
        <img src="search_icon.png" class="input_icon">
    </div>
    
    <script>
    
    var icon = document.querySelector(".input_icon");
    var input = document.querySelector(".header_search");
        
    input.addEventListener("focus",insideRemover);
        
    function insideRemover() {
        icon.style.display = "none";
        input.placeholder = "";
        window.addEventListener("mousedown",function(event) {
            if (event.target.className != "header_search" && input.value == "") {
                input.placeholder = "      Поиск";
                icon.style.display = "block";
            }    
        })
    }
        
    </script>
            <nav>
                <ul type=none>
                    <li><a href="">Сотрудничество</a></li>
                    <li><a href="">Магазины</a></li>
                    <li><a href="">Помощь</a></li>
                    <li><a href="">Регистрация</a></li>
                </ul>
            </nav>
        </div>
    </header>

</body>
</html>