how to make a web page responsive using css code example

Example 1: responsive html

@media (max-width: 530px){
    .CLASSHERE {
        padding: 10px 110px;
        margin-left: 365px;
        margin-bottom: 30px;
        font-size: medium;
        text-align: center;
    }
}

Example 2: make it responsive

<div id="gallery">
            <div class="showcase-images">
                <div class="showcase-block">
            <img id="show-img" src="images/showcase/tabs.png" alt="Tabs">
            </div>
            </div>
            <nav>
            <ul id="main">
                <li id="tabs"><a href="#">Tab</a></li>
                <li id="login"><a href="#">Login</a></li>
                <li id="forum"><a href="#">Forum</a></li>
            </ul>
        </nav>
        </div>