標籤：
You can target an element that has no child elements by using the :empty pseudo-class. With browser support down to IE9, it‘s solid, easy way to select empty elements without any additional markup.
Be aware that whitespace is considered a "child", so :empty will not work if the element has no children, but has space between the opening and closing tags.
<!DOCTYPE html><html><head> <link href="https://fonts.googleapis.com/css?family=Work+Sans" rel="stylesheet"> <link rel="stylesheet" href="style.css"></head><body> <div class="Alert"> <p>Success! Your profile has been updated.</p> </div> <!-- This empty alert box won‘t be show--> <div class="Alert"></div></body></html>
.Alert:not(:empty) { border: 3px solid darkgreen; margin: 1em; padding: 1em; background-color: seagreen; color: white; border-radius: 4px;}.Alert:empty{ display:none;}
[CSS] Target empty elements using the :empty pseudo-class
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