Code
css3
/* Interactive states */
a:hover { text-decoration: underline; }
input:focus { border-color: #1976d2; }
button:active { transform: scale(0.97); }
/* Structural selectors */
li:first-child { font-weight: bold; }
li:last-child { border-bottom: none; }
li:nth-child(odd) { background: #f5f5f5; }
li:nth-child(3n+1) { color: red; }
/* Negation and matching */
input:not([type="submit"]) { width: 100%; }
a[href^="https"] { color: green; }
/* Form state */
input:disabled { opacity: 0.5; }
input:checked + label { font-weight: bold; }
input:placeholder-shown { border-color: #ccc; }
/* Empty element */
.box:empty::before { content: "No content"; }