Fixed various style bugs with the gantt chart

src/styles/gantt.scss

@@ -148,6 +148,7 @@ $gantt-vertical-border-color: lighten($grey, 45);
     min-height: 0;
     top: 10vh;
     right: 10vw;
+    z-index: 5;
 
     .card-content {
       max-height: 60vh;

src/styles/theme.scss

@@ -240,6 +240,7 @@ h1,h2,h3,h4,h5,h6{
 
 .navbar.main-theme {
   background: $light-background;
+  z-index: 30 !important;
 }
 
 .switch-view {