The CSS to make the dialog
<meta charset="utf-8" & gt;
Document <style>/* & lt; ! - making quadrilateral - & gt; */. Box {margin - left: 50 px; width: 200px; Height: 60 px; Border: 1 px solid # 333333;/* relative behaviour is relative and absolute absolute positioning collocation use */position: relative; }/* */solid triangle. Box: before {position: absolute; Left: - 20 px; Top: 10 px; Content: ""; Border - right: 20 px solid # 333333; Border - top: 20 px solid transparent; Border - bottom: 20 px solid transparent; }/* */hollow triangle. Box: after {position: absolute; Left: - 19 px; Top: 11 px; Content: ""; Border - right: 19 px solid white; Border - top: 19 px solid transparent; Border - bottom: 19 px solid transparent; } & lt;/style>
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5. Using the left top value change position for the effect of the hollow triangle - & gt;
