<div id="container2">
  <div id="container1">
    <div id="col1">
      <div class="float-content">col1</div>
      <div class="float-content">1</div>
      <div class="float-content">2</div>
      <div class="float-content">3</div>
      <div class="float-content">4</div>
      <div class="float-content">5</div>
      <div class="float-content">6</div>
      <div class="float-content">7</div>
      <div class="float-content">8</div>
      <div class="float-content">9</div>
    </div>
    <div id="col2">
      <div class="float-content">col2</div>
      <div class="float-content">1</div>
      <div class="float-content">2</div>
      <div class="float-content">3</div>
      <div class="float-content">4</div>
      <div class="float-content">5</div>
      <div class="float-content">6</div>
      <div class="float-content">7</div>
      <div class="float-content">8</div>
      <div class="float-content">9</div>
      <div class="float-content">10</div>
      <div class="float-content">11</div>
      <div class="float-content">12</div>
      <div class="float-content">13</div>
      <div class="float-content">14</div>
      <div class="float-content">15</div>
      <div class="float-content">16</div>
      <div class="float-content">17</div>
      <div class="float-content">18</div>
      <div class="float-content">19</div>
      <div class="float-content">0</div>
      <div class="float-content">1</div>
      <div class="float-content">2</div>
      <div class="float-content">3</div>
      <div class="float-content">4</div>
      <div class="float-content">5</div>
      <div class="float-content">6</div>
      <div class="float-content">7</div>
      <div class="float-content">8</div>
      <div class="float-content">9</div>
      <div class="float-content">10</div>
      <div class="float-content">11</div>
      <div class="float-content">12</div>
      <div class="float-content">13</div>
      <div class="float-content">14</div>
      <div class="float-content">15</div>
      <div class="float-content">16</div>
      <div class="float-content">17</div>
      <div class="float-content">18</div>
      <div class="float-content">19</div>
    </div>
  </div>
</div>

html, body {
  margin: 0;
  padding: 0;
}

#container2 {
    float:left;
    width:100%;
    background:yellow;
}

#container1 {
    float:left;
    width:100%;
    background: red;
    position: relative; /* 추가 */
    right: 70%; /* 추가 */
}
#col1 {
    float:left;
    width:30%;
}
#col2 {
    float:left;
    width:70%;
}