A CodePen by Geoff Alday. - All graphical elements created with CSS.

index.html

<div class="box">
  <div class="box-top"></div>
  <div class="box-body">
    <div class="heading">
      <h1>Introduction</h1>
    </div>
    <div class="content">
      <p>The passion for play is probably as old, and will be as enduring, as the race of man. Some of us are too timid to risk a dollar, but the percentage of people in this feverish nation who would not enjoy winning  one is very small. The passion culminates in the professional. He would rather play than eat. Winning is not his sole delight. Some one has remarked that there is but one pleasure in life greater than winning, that is, in making the hazard.</p>
    </div>
  </div>
  <div class="box-bottom"></div>
</div>

style.css

body { 
  background: #eee; 
  font-family: Arial; 
  padding: 50px; }

.box { 
  width: 500px; }

.box .box-top { 
  height: 10px;
  width: 492px;
  background: #fff;
  position: relative; 
  background: #fff; 
  border-left: 1px solid #eaebeb; }

.box .box-top:before { 
  content: ''; 
  position: absolute; 
  top: 0; 
  right: -7px; 
  width: 0; 
  height: 0; 
  border-bottom: 7px solid #bebebe; 
  border-right: 7px solid transparent; }

.box .box-top:after { 
  content: ''; 
  position: absolute; 
  top: 7px; 
  right: -7px; 
  width: 7px; 
  height: 3px; 
  background: #bebebe; }

.box .box-bottom {
  margin-left: 8px;
  height: 7px; 
  background: #bebebe; position: relative; }

.box .box-bottom:before { 
  content: ''; 
  position: absolute; 
  top: 0; 
  left: -7px; 
  width: 0; 
  height: 0; 
  border-top: 7px solid #bebebe; 
  border-left: 7px solid transparent; }

.box .box-body { 
  background: #fff;
  border-right: 7px solid #BEBEBE; }

.box .heading { 
  width: 467px;
  background: #99cc33;
  margin: 0 0 0 -9px; 
  padding: 4px 8px 6px 15px; 
  position: relative; 
  border-bottom: 2px solid #BEBEBE; 
  border-right: 2px solid #BEBEBE; }

.box .heading:before { 
  content: ''; 
  position: absolute; 
  bottom: -2px; 
  left: 0; 
  width: 8px; 
  height: 2px; 
  background: #7ab71e; }

.box .heading:after { 
  content: ''; 
  position: absolute; 
  bottom: -10px; 
  left: 0; 
  width: 0; 
  height: 0; 
  border-top: 8px solid #87c027; 
  border-left: 8px solid transparent; }

.box .heading h1 { 
  color: #fff; 
  font-size: 20px; }

.box .content { 
  padding: 15px 20px 20px; 
  font-size: 14px; 
  line-height: 150%; }