what do I need to do to adapt the div width of the middle input? Is there any good way to do this without knowing the total width
  <header class="header-div">
      <div class="header-top">
        <div class="header-img">
          <img src="../../static/position.png" alt="" style="margin-top: -5px">
        </div>
        <span></span>
        <div>
          <div class="header-img">
            <img src="../../static/searrch.png" alt="">
          </div>
          <input type="text" placeholder="">
        </div>
        <div class="header-img">
          <img src="../../static/email.png" alt="" >
        </div>
      </div>
    </header>
I set the width of both sides as rem, so I don"t know exactly how much it is
./*** rem   scss ***/
@function px2rem($px, $base-font-size: 75px) {
    @return ($px / $base-font-size) * 1rem;
}
/*** rem end ***/
//
.div {
        width: px2rem(40px);
        height: px2rem(40px);
 }
I can"t always set the width for the middle div
width: calc(100% - px2rem(XXX));
. 
 ask everyone to take a look at it for me 
