I try to put the title on the center of the div of "introduction" div
#introduction {
box-sizing: border-box;
height: 800px;
background-repeat: no-repeat;
background-size: cover;
background-position: 50% 50%;
background-image: url(https://www.planetware.com/wpimages/2020/02/france-in-pictures-beautiful-places-to-photograph-eiffel-tower.jpg);
}
#introduction h1 {
margin: 35% auto;
position: relative;
width: 100%;
text-align: center;
}
<div id="introduction">
<h1>Hanzi Li's Blog</h1>
</div>
by margin: 35% auto; I thought the title should be put 35% relative to the introduction div, but it seems that it is 35% relative to the screen: