Resolve "Subsite: Learning Materials"

Closes #236 (closed)

Improve the Organization of the learning materials a bit.

_sass/common/_table.scss

+
+table{
+    margin: 1 rem;
+    border-collapse: collapse;
+    border: 0.1rem solid $color-helmholtz-blue;
+
+    tr {
+        &:nth-child(even){
+            background-color: rgba($color-helmholtz-bright-blue, 0.125);
+        }
+
+        &:hover {
+            background-color: rgba($color-helmholtz-blue, 0.25);
+        }
+    }
+
+    th {
+        color: $color-content-light-gray;
+        background-color: $color-helmholtz-blue;
+
+    }
+
+    td, th {
+        padding: 0.2rem 0.5rem;
+    }
+}