-child(3) img {width: 100px; height: 35px; margin-bottom: 22.5px;}
li:nth-child(4) img {width: 100px; height: 20px; margin-bottom: 30px;}
</style>
</head>
<body>

<ol>
<li><img src="i/chrome.jpg" alt=""><b>height: 100px</b></li>
<li><img src="i/chrome.jpg" alt=""><b>height: 60px</b></li>
<li><img src="i/chrome.jpg" alt=""><b>height: 35px</b></li>
<li><img src="i/chrome.jpg" alt=""><b>height: 20px</b></li>
</ol>

</body>
</html>