implmented the button colors of halloween, future,spring,antarctic

src/client/styles/scss/theme/antarctic.scss

@@ -112,6 +112,13 @@ html[dark] {
   @import 'apply-colors';
   @import 'apply-colors-light';
 
+  //Button
+  .grw-three-stranded-button {
+    .btn.btn-outline-primary {
+      @include three-stranded-button(darken($primary, 30%), lighten($primary, 65%), lighten($primary, 70%));
+    }
+  }
+
   .table {
     background-color: $themelight;
   }

src/client/styles/scss/theme/future.scss

@@ -89,6 +89,13 @@ html[dark] {
   @import 'apply-colors';
   @import 'apply-colors-dark';
 
+  //Button
+  .grw-three-stranded-button {
+    .btn.btn-outline-primary {
+      @include three-stranded-button(lighten($primary, 10%), $primary, darken($primary, 10%), darken($primary, 20%));
+    }
+  }
+
   // headers
   @for $i from 1 through 6 {
     h#{$i} {

src/client/styles/scss/theme/halloween.scss

@@ -107,6 +107,13 @@ html[dark] {
   @import 'apply-colors';
   @import 'apply-colors-dark';
 
+  //Button
+  .grw-three-stranded-button {
+    .btn.btn-outline-primary {
+      @include three-stranded-button(lighten($primary, 35%), $primary, lighten($primary, 5%), darken($primary, 20%));
+    }
+  }
+
   // Table
   .table {
     color: $color-global;

src/client/styles/scss/theme/spring.scss

@@ -93,6 +93,13 @@ html[dark] {
   @import 'apply-colors';
   @import 'apply-colors-light';
 
+  //Button
+  .grw-three-stranded-button {
+    .btn.btn-outline-primary {
+      @include three-stranded-button(darken($primary, 50%), lighten($primary, 5%), lighten($primary, 10%));
+    }
+  }
+
   .growi:not(.login-page) {
     // add background-image
     #page-wrapper,