<style>
.size-40px {
font-size: 40px;
}
.color-red {
color: red;
}
#second {
font-style: italic;
}
</style>
<body>
abcd<span class="color-red">foo</span>123456<br>
abcd<span id="second" class="size-40px">foo</span>123456<br>
abcd<span class="size-40px color-red">foo</span>123456
</body>