a {text-decoration: none; display: inline-block; padding: 8px 12px;}
a:hover {background-color: lightblue; color: black;}
.previous {background-color: blue; color: white;}
.retc {background-color: red; color: white;}
.next {background-color: blue; color: white;}
.round {border-radius: 50%;}
.retc {border-radius: 20%;}
Graphical Abstract
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