<header class="layout">
  <mat-toolbar>
    <a href="https://github.com/mrWh1te/ngExcel" target="_blank" rel="noreferrer" class="github-corner" aria-label="View source on GitHub" title="View source on GitHub">
      <svg width="50" height="50" viewBox="0 0 250 250" style="fill:#151513; color:#fff; position: absolute; top: 0; border: 0; left: 0; transform: scale(-1, 1);" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg><style>.github-corner:hover .octo-arm{animation:octocat-wave 560ms ease-in-out}@keyframes octocat-wave{0%,100%{transform:rotate(0)}20%,60%{transform:rotate(-25deg)}40%,80%{transform:rotate(10deg)}}@media (max-width:500px){.github-corner:hover .octo-arm{animation:none}.github-corner .octo-arm{animation:octocat-wave 560ms ease-in-out}}</style></a>
    <h2 fxFlex="1 1 auto" style="text-align: center;">ngExcel</h2>
    <span class="reset icon" (click)="resetSpreadsheet()">
      <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 50 50"><path d="M 25 2 C 12.321124 2 2 12.321124 2 25 C 2 37.678876 12.321124 48 25 48 C 37.678876 48 48 37.678876 48 25 A 2.0002 2.0002 0 1 0 44 25 C 44 35.517124 35.517124 44 25 44 C 14.482876 44 6 35.517124 6 25 C 6 14.482876 14.482876 6 25 6 C 30.475799 6 35.391893 8.3080175 38.855469 12 L 35 12 A 2.0002 2.0002 0 1 0 35 16 L 46 16 L 46 5 A 2.0002 2.0002 0 0 0 43.970703 2.9726562 A 2.0002 2.0002 0 0 0 42 5 L 42 9.5253906 C 37.79052 4.9067015 31.727675 2 25 2 z"></path></svg>
    </span>
  </mat-toolbar>
</header>
<section class="main-child-view">
  <router-outlet></router-outlet>
</section>

./layout.component.scss

// Vars
@import '../../../../styles/layout';
@import '../../../../styles/colors';

//
// Base Layout
:host {
  display: block;
  height: 100vh;
}

header.layout {
  -moz-box-shadow:    2px -5px 6px 5px $gray;
  -webkit-box-shadow: 2px -5px 6px 5px $gray;
  box-shadow:         2px -5px 6px 5px $gray;

  .icon {
    -webkit-touch-callout: none; /* iOS Safari */
    -webkit-user-select: none; /* Safari */
     -khtml-user-select: none; /* Konqueror HTML */
       -moz-user-select: none; /* Firefox */
        -ms-user-select: none; /* Internet Explorer/Edge */
            user-select: none; /* Non-prefixed version, currently
                                  supported by Chrome and Opera */
    &:hover {
      cursor: pointer;
    }
  }
}

.reset {
  margin-left: 1rem;
  svg {
    width: 1rem;
  }
}

body {
  overflow: hidden;
}

.main-child-view {
  height: calc(100vh - #{$header-height});
  // overflow-y: auto;
}

.github-corner {
  opacity: .8;
}