The :only-child pseudo-class selector property in CSS represents an element that has a parent element and whose parent element has […]

The :only-of-type pseudo-class selector in CSS represents any element that has no siblings of the given type. p:only-of-type { color: […]

p:only-of-type { font-size: 120% }

The :optional pseudo class targets inputs (including <select>s) that are not specifically set as required (do not have the required attribute). This can be useful when you […]

.element:optional { background: #f8a100; }

The :out-of-range pseudo selector in CSS matches input elements when their value is outside the range specified as being acceptable. […]

input:out-of-range { border: 5px solid red; }