Example code sharing for CSS pseudo-class combination usage

Using pseudo-class combination, you can use CSS instead of JS to achieve the goal, less JS

. textarea:empty:before {    display:block;    Content: ' Please enter ';    Color: #ababab;    font-size:15px;    Text-align:left;} <br>//said: When the textarea element is empty, there is no input, there is "please enter" this phrase to display  . textarea:focus:before {    display:none;} <br>//when the textarea element is focused, just use the before pseudo-class add "Please enter" will hide the <br><br>.textarea:empty:after {content: ' Please fill in carefully. ';   Color: #ababab;   font-size:11px;   Text-align:left;}. Textarea:focus:focus {    display:none;} first-child:after.order:empty+.a {    display:block;} When the <br>//order element is empty, the element a below it shows