Can only be used inside the selector in which it is created in.
:root is a pseudo-class selector that matches the root element of the document.
This is typically the html element.
Final Code
<style>:root{/* Only change code below this line */--penguin-belly:pink;/* Only change code above this line */}body{background:var(--penguin-belly,#c6faf1);}.penguin{--penguin-skin:gray;--penguin-beak:orange;position:relative;margin:auto;display:block;margin-top:5%;width:300px;height:300px;}.right-cheek{top:15%;left:35%;background:var(--penguin-belly,white);width:60%;height:70%;border-radius:70%70%60%60%;}.left-cheek{top:15%;left:5%;background:var(--penguin-belly,white);width:60%;height:70%;border-radius:70%70%60%60%;}.belly{top:60%;left:2.5%;background:var(--penguin-belly,white);width:95%;height:100%;border-radius:120%120%100%100%;}.penguin-top{top:10%;left:25%;background:var(--penguin-skin,gray);width:50%;height:45%;border-radius:70%70%60%60%;}.penguin-bottom{top:40%;left:23.5%;background:var(--penguin-skin,gray);width:53%;height:45%;border-radius:70%70%100%100%;}.right-hand{top:0%;left:-5%;background:var(--penguin-skin,gray);width:30%;height:60%;border-radius:30%30%120%30%;transform:rotate(45deg);z-index:-1;}.left-hand{top:0%;left:75%;background:var(--penguin-skin,gray);width:30%;height:60%;border-radius:30%30%30%120%;transform:rotate(-45deg);z-index:-1;}.right-feet{top:85%;left:60%;background:var(--penguin-beak,orange);width:15%;height:30%;border-radius:50%50%50%50%;transform:rotate(-80deg);z-index:-2222;}.left-feet{top:85%;left:25%;background:var(--penguin-beak,orange);width:15%;height:30%;border-radius:50%50%50%50%;transform:rotate(80deg);z-index:-2222;}.right-eye{top:45%;left:60%;background:black;width:15%;height:17%;border-radius:50%;}.left-eye{top:45%;left:25%;background:black;width:15%;height:17%;border-radius:50%;}.sparkle{top:25%;left:15%;background:white;width:35%;height:35%;border-radius:50%;}.blush-right{top:65%;left:15%;background:pink;width:15%;height:10%;border-radius:50%;}.blush-left{top:65%;left:70%;background:pink;width:15%;height:10%;border-radius:50%;}.beak-top{top:60%;left:40%;background:var(--penguin-beak,orange);width:20%;height:10%;border-radius:50%;}.beak-bottom{top:65%;left:42%;background:var(--penguin-beak,orange);width:16%;height:10%;border-radius:50%;}.penguin*{position:absolute;}</style><divclass="penguin"><divclass="penguin-bottom"><divclass="right-hand"></div><divclass="left-hand"></div><divclass="right-feet"></div><divclass="left-feet"></div></div><divclass="penguin-top"><divclass="right-cheek"></div><divclass="left-cheek"></div><divclass="belly"></div><divclass="right-eye"><divclass="sparkle"></div></div><divclass="left-eye"><divclass="sparkle"></div></div><divclass="blush-right"></div><divclass="blush-left"></div><divclass="beak-top"></div><divclass="beak-bottom"></div></div></div>