Add theme support, light theme, and edgeless light

sass/includes/buttons.sass

@@ -1,82 +0,0 @@
-@use "sass:selector"
-@use "colors.sass" as c
-
-@mixin button-base
-  -webkit-appearance: none
-  -moz-appearance: none
-  color: c.$fg-bright
-  border: none
-  border-radius: 4px
-  padding: 8px
-  margin: 0
-  text-decoration: none
-  line-height: 1.25
-
-  @at-root #{selector.unify(&, "select")}
-    padding: 8px 27px 8px 8px
-    background: url(/static/images/arrow-down-wide.svg) right 53% no-repeat c.$bg-accent-x
-
-  @at-root #{selector.unify(&, "a")}
-    padding: 7px 8px
-
-  @at-root #{selector.unify(&, "button")}
-    cursor: pointer
-
-  .button-icon
-    position: relative
-    top: 3px
-    margin-right: 8px
-    margin-left: 2px
-
-@mixin button-bg
-  @include button-base
-
-  background-color: c.$bg-accent-x
-
-@mixin border-button
-  @include button-bg
-
-  border: 1px solid c.$edge-grey
-
-@mixin button-size
-  margin: 4px
-  font-size: 16px
-
-@mixin button-hover
-  &:hover
-    background-color: c.$bg-accent
-
-  &:active
-    background-color: c.$bg-dark
-
-.base-border-look
-  @include border-button
-
-.border-look
-  @include border-button
-  @include button-size
-  @at-root #{selector.unify(&, "a, button")}
-    @include button-hover
-
-.menu-look
-  @include button-size
-  -webkit-appearance: none
-  -moz-appearance: none
-  color: c.$fg-bright
-  text-decoration: none
-  line-height: 1.25
-  margin: 0
-  padding: 8px 20px
-  background: c.$bg-accent
-  border: solid c.$bg-darker
-  border-width: 1px 0px 0px
-  text-align: left
-
-  &:last-child
-    border-width: 1px 0px 1px
-
-  &:hover
-    background: c.$bg-accent-x
-
-  &:active
-    background: c.$bg-darker