CSS Playground

a[href^=http] // starts witha[href$=pdf] // ends witha[href*=pdf] //anywhere pdfa[href~=unicorn] //full word will not match unicorns

// and label that comes immediately after checked input element of type checkboxinput[type=checkbox]:checked + label{    color: red;}

body{    counter-reset: invalidCount;}:invalid {    background-color: pink;    counter-increment: invalidCount;}
p:before{    content: "You have " counter(invalidCount) " invalid entries"}

:first-of-type{}:first-child{}:last-of-type{}:last-child{}:only-of-type{}:only-child{}