fix color of icon in navbar on mobile using CSS filter

Author: mojavelinux

src/css/header.css

@@ -176,11 +176,18 @@ body {
 
 .navbar-item .icon img,
 .navbar-item .icon svg {
-  fill: currentColor;
   width: inherit;
   height: inherit;
 }
 
+.navbar-item .icon img {
+  filter: invert(10%);
+}
+
+.navbar-item .icon svg {
+  fill: currentColor;
+}
+
 .navbar-link {
   padding-right: 2.5em;
 }
@@ -315,6 +322,10 @@ body {
     padding-left: 0;
   }
 
+  .navbar-item .icon img {
+    filter: invert(100%);
+  }
+
   .navbar-dropdown {
     background: var(--navbar-menu-background);
     border: 1px solid var(--navbar-menu-border-color);

src/img/octicons-16.svg

@@ -86,7 +86,7 @@
         </div>
         --}}
         <a class="navbar-item" href="https://github.com/asciidoctor" target="_blank" rel="noopener">
-          <span class="icon"><img src="{{{uiRootPath}}}/img/octicons-16.svg#view-mark-github-w"></span>
+          <span class="icon"><img src="{{{uiRootPath}}}/img/octicons-16.svg#view-mark-github"></span>
         </a>
       </div>
     </div>