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<html><head><style> #main { width: 270px; height: 300px; border: 1px solid black; display: flex;}#main div { flex: 1;}#myBlueDiv { animation: mymove 5s infinite;}@keyframes mymove { 50% {flex: 3;}}</style></head><body><h1>Animation of flex</h1><p>Gradually change the flex property of the BLUE div element from 1 to 3, and back:<p><div id="main"> <div style="background-color:coral;">RED</div> <div style="background-color:lightblue;" id="myBlueDiv">BLUE</div> <div style="background-color:lightgreen;">GREEN</div></div></body></html>