html:<div class="lx"><img src="img/replace_me.jpg" alt=""></div>
css:
.lx{transform:rotate(45deg)width:400pxheight:400pxoverflow:hiddenvertical-align: middletext-align: centermargin:100px autodisplay:flex}
.lx img{transform:rotate(-45deg)max-width:100%max-height:100%}
可以画两个等腰三角形,等腰三角形代码#ID {width: 0
height: 0
border-left: 50px solid transparent
border-right: 50px solid transparent
border-bottom: 100px solid red}