<html><head><style>#grad1 { height: 200px; background-image: linear-gradient(to right, red, orange, yellow, green, blue, indigo, violet);}</style></head><body><h1>线性渐变 - 彩虹效果</h1><div id="grad1" style="text-align:center;margin:auto;color:#888888;font-size:40px;font-weight:bold">渐变背景</div></body></html>