Add theme support, light theme, and edgeless light

sass/includes/nav.sass

@@ -1,51 +0,0 @@
-@use "colors.sass" as c
-@use "buttons.sass" as *
-@use "_dimensions.sass" as dimensions
-
-.main-nav
-  background-color: c.$bg-accent
-  display: flex
-  padding: 8px
-  box-shadow: 0px 0px 20px 5px rgba(0, 0, 0, 0.1)
-
-  +dimensions.thin
-    display: block
-
-  .links
-    display: flex
-
-    +dimensions.thin
-      margin-bottom: 4px
-      padding: 1px
-
-  .link
-    @include button-base
-    text-decoration: none
-    margin: 1px 8px 1px 0px
-    font-size: 20px
-    display: flex
-    align-items: center
-
-    &.home
-      font-weight: bold
-
-    &, &:visited
-      color: #fff
-
-    &:focus, &:hover
-      background-color: c.$bg-accent-x
-
-  .search-form
-    display: flex
-    flex: 1
-    align-items: center
-
-    .search
-      @include button-bg
-      padding: 10px
-      flex: 1
-      margin: 1px
-
-      &:hover, &:focus
-        border: 1px solid c.$edge-grey
-        margin: 0px