body { text-align: center; font-family:sans-serif, verdana; color:yellow;}
body { width: 100vw; min-height: 100vh; background: url("1920-pixabay.jpg"); background-size: cover; }
#white { font-size:1.2em;color:white;}
#siz{ font-size:1.5em; }
#img1 {  margin: auto; width:60%; margin-top: 20px;}
@media all and (min-width: 100px) and (max-width: 320px) { .mydiv { margin: auto;  width:70%; }  }
@media all and (min-width: 321px) and (max-width: 641px) { .mydiv { margin: auto;  width:50%; }  }
@media all and (min-width: 642px) and (max-width: 1280px) { .mydiv { margin: auto;  width:30%; } }
@media all and (min-width: 1281px)  { .mydiv { margin: auto;  width:20%; } }