[解決済み】2つのdivを隣り合わせにするCSS

#parent {
  display: flex;
}
#narrow {
  width: 200px;
  background: lightblue;
  /* Just so it's visible */
}
#wide {
  flex: 1;
  /* Grow to rest of container */
  background: lightgreen;
  /* Just so it's visible */
}

<div id="parent">
  <div id="wide">Wide (rest of width)</div>
  <div id="narrow">Narrow (200px)</div>
</div>

#narrow {
  float: right;
  width: 200px;
  background: lightblue;
}
#wide {
  float: left;
  width: calc(100% - 200px);
  background: lightgreen;
}

<div id="parent">
  <div id="wide">Wide (rest of width)</div>
  <div id="narrow">Narrow (200px)</div>
</div>