How to used position fixed without overlapping the width of container

Question

Here is the codepen. As you can see using position: sticky; the div width is not overlapping. However when I tried using position: fixed the div width is overlapping. Can anyone help me with how to achieve it? My goal is I what my footer class to fixed at the bottom even I scroll.

* {
-webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    font-size: inherit;  
}

.left {
    position: fixed;
    top: 0;
    width: 43px;
    left: 0;
    bottom: 0;
    /* border-right: 1px solid #e8edf3; */
    background-color: red;
    padding: 6px;
    overflow: hidden;
    transition: .18s ease-out width;
}

.main {
    margin: 0;
    padding: 0;
    position: absolute;
    top: 0;
    left: 42px;
    right: 0;
    bottom: 0;
    overflow: auto;
    transition: .22s ease left;
    background: green;
}

.tool {
    display: flex;
    padding: 3px 4px;
    /* box-sizing: border-box; */
    align-items: center;
    width: 100%;
    border-bottom: 1px solid #e8edf3;
    position: sticky;
    top: 0;
    background-color: #ffffff;
    z-index: 13;
    justify-content: space-between;
}

.footer {
    padding: 3px 4px;
    align-items: center;
    width: 100%;
    border-bottom: 1px solid #e8edf3;
    position: fixed;
    bottom: 0;
    background-color: #ffffff;
    z-index: 13;
    display: flex;
    justify-content: space-between;
}

<div class="left">

</div>
<div class="main">
  <div class="tool">
    <div class="test">Test toolbar design</div>
        <div class="test">Test toolbar design</div>
  </div>
  <div class="footer">
    <div class="test">Test footer design</div>
        <div class="test">Test footer design</div>
  </div>
<div>