Replace Sass with PostCSS, include imports and nesting

assets/sass/base/base.sass

@@ -1,36 +0,0 @@
-a
-  color: inherit
-  text-decoration: none
-
-  &:focus,
-  &:hover
-    text-decoration: underline
-
-main a
-  text-decoration: underline
-
-  &:focus,
-  &:hover
-    text-decoration: none
-
-h1, h2, h3
-  @apply mb-2
-
-.content
-  h2,
-  h3
-    @apply mt-6
-
-p,
-ul,
-ol,
-blockquote,
-table,
-pre
-  @apply mb-6
-
-.element-invisible
-  @apply absolute overflow-hidden break-normal
-  clip: rect(1px, 1px, 1px, 1px)
-  height: 1px
-  width: 1px

assets/sass/base/images.sass

@@ -1,12 +0,0 @@
-img
-  &.with-border
-    @apply border border-solid border-grey-light
-
-  &.with-padding
-    @apply p-1
-
-  &.avatar
-    @apply border p-1 rounded-full
-
-svg
-  fill: currentColor

assets/sass/base/vue.sass

@@ -1,20 +0,0 @@
-[v-cloak]
-  .v-cloak-block
-    @apply block
-
-  .v-cloak-inline
-    @apply inline
-
-  .v-cloak-inline-block
-    @apply inline-block
-
-  .v-cloak-hidden
-    @apply hidden
-
-  .v-cloak-invisible
-    @apply invisible
-
-.v-cloak-block,
-.v-cloak-inline,
-.v-cloak-inline-block
-  @apply hidden