<html><head><style> .div1 { width: 300px; height: 100px; border: 1px solid blue; box-sizing: border-box;}.div2 { width: 300px; height: 100px; padding: 50px; border: 1px solid red; box-sizing: border-box;}</style></head><body><div class="div1">现在，两个 div 的尺寸是一样的！</div><br><div class="div2">Hello！</div></body></html>