Div 不应超过 Div，背景图像内有 div

body {
  margin: 0;
  padding: 0;
  /*background-color: blue;*/
}

.divider {
  background-color: #be2b27;
  width: 100%;
  height: 100px;
  position: absolute;
  display: block;
  padding: 0;
}

.divider h1 {
  font-family: "Nexa Light";
  font-size: 2em;
  color: white;
  text-align:left;
  padding-left: 10px;
}

.lorem-text {
  font-family: "Menlo";
  font-size: 1.2em;
  color: white;
}

.start-section {
   margin-top: 30px;
   /* position: absolute; */
   padding-left: 20px;
   padding-top: 20px;
}


#start-bg {
  background-image: url(water.jpg);
  background-color:#9abee1;
  background-repeat: round;
  height:100%;
  position: absolute;
}

#home-head {
  font-family: 'Nexa Light';
  /* font-size: ; */
  padding-top: 30px;
  color: white;
}

.nav { }

<div id="start-bg">
  <!--<div class="nav"...>...</div>-->
  <div class="start-section">
    <h1 id="home-head">Landing Page</h1>
    <p class="lorem-text">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec ornare est in maximus vestibulum.
    Mauris eu tincidunt quam.<br> In commodo neque id tortor mattis, non consectetur ante tincidunt.
    Nunc ultrices ultricies purus, id finibus justo eleifend sit amet.<br>
    Sed in iaculis libero, et gravida nibh.
    Proin mollis, nibh eu rhoncus scelerisque, orci ex posuere mi, id pharetra purus est suscipit sapien.
    Aliquam fermentum dignissim ultricies. Cras vitae neque tincidunt, tristique neque at, ornare leo.<br>
    Integer gravida lectus sed venenatis auctor. Vestibulum sed ligula eget dui ultrices luctus.<br>
    Etiam dapibus auctor sollicitudin. Nam vel dui non lorem semper scelerisque. Donec sed condimentum mauris.
    Maecenas ac enim sit amet orci sodales porta.
    </p>
    <img src="http://via.placeholder.com/350x150">
    <img src="http://via.placeholder.com/350x150">
    <img src="http://via.placeholder.com/350x150"><br>
    <img src="http://via.placeholder.com/350x150">
    <img src="http://via.placeholder.com/350x150">
    <img src="http://via.placeholder.com/350x150"><br>
  </div>
</div>
<div class="divider">
  <h1>About</h1>
</div>