CSS是网页设计中常用的样式表语言，它可以用来控制和美化HTML元素的布局、字体、颜色和其他样式特征。以下是常用的CSS代码：

/*设置HTML元素全局默认样式*/html {font-size: 16px;font-family: Arial, Helvetica, sans-serif;color: #333;}/*设置超链接样式*/a {color: #0066cc;text-decoration: none;}a:hover {text-decoration: underline;}/*设置列表样式*/ul {list-style-type: disc; /*圆点*/}ol {list-style-type: decimal; /*数字*/}li {margin-left: 15px;}/*设置表格样式*/table {border-collapse: collapse;}th, td {border: 1px solid #ccc;padding: 5px;}/*设置盒子模型属性*/.box {width: 200px;height: 150px;margin: 10px;padding: 20px;border: 1px solid #ccc;box-sizing: border-box; /*元素宽高包含边框和内边距*/}/*设置背景和文本样式*/.bg {background-color: #f5f5f5;background-image: url(bg.png);background-repeat: repeat;color: #666;}/*设置浮动和定位属性*/.left {float: left;width: 50%;}.right {float: right; width: 50%;}.absolute {position: absolute;top: 50px;left: 50px;}/*设置动画效果*/.rotate {animation: rotate 2s linear infinite;}@keyframes rotate {from {transform: rotate(0deg);}to {transform: rotate(360deg);}}