body,html{min-height:100%}#logo{margin-top:1%;margin-left:1%;z-index:-1}#left-div{display:flex;flex-wrap:nowrap;padding-right:100px}#background{background-image:url(picture/HD_BG_2.png);background-repeat:no-repeat;background-position:center;width:1200px;height:900px;background-size:cover}#description_div{max-width:560px;max-height:280px;height:280px;float:right;padding-top:23%;padding-left:150px;color:#000}#identity_div{width:500px;margin-top:60%;margin-right:30%}#role{max-width:fit-content;margin-top:0;margin-left:auto;margin-right:auto}#teacher_btn{background-color:#0071bc;padding-left:60px;padding-right:60px;font-size:28px;color:#fff}#student_btn{background-color:#29abe2;padding-left:60px;padding-right:60px;font-size:28px;color:#fff}.language_link{font-size:20px}@media all and (max-width:480px){#description_div{width:100%}#identity_div{width:100%;margin-top:10%}#background{background-image:url(picture/HD_BG_2.png);background-size:cover}#role{max-width:fit-content;margin-top:0;margin-left:auto;margin-right:auto;flex-wrap:wrap}h1{font-size:30px}h4{font-size:20px}.language_link{font-size:15px}}@media all and (max-width:780px){#description_div{margin-left:auto;margin-right:auto;margin-bottom:auto}#identity_div{width:100%;margin-left:0;margin-top:400px}#role{max-width:fit-content;margin-top:0;margin-left:auto;margin-right:auto;flex-wrap:wrap}#background{background-image:url(picture/HD_BG_2.png);background-size:cover;max-width:100%;height:fit-content;padding-top:0;padding-bottom:0;display:flex;flex-wrap:wrap}h1{font-size:30px}h4{font-size:20px}.language_link{font-size:15px}.footer{min-width:100%;overflow:visible;bottom:0}}