replace various SASS button.small extending by button-small-basic mixin

sass/base/_utils.sass

@@ -56,6 +56,12 @@
 	&:hover
 		border-color: darken($color, $hover-border-color-darken-amount)
 
+@mixin button-small-basic
+	padding:  .5rem
+	font-weight: 700
+	font-size: .7rem
+	line-height: .7rem
+
 button, a.button
 	@include button-basic
 	&.color-1
@@ -63,10 +69,7 @@ button, a.button
 	&.color-2
 		@include button-color-basic(2)
 	&.small
-		padding:  .5rem
-		font-weight: 700
-		font-size: .7rem
-		line-height: .7rem
+		@include button-small-basic
 	&.light
 		background: #eee
 		border-color: darken(#eee, 5%)

sass/layout/_modal.sass

@@ -112,7 +112,7 @@ $header-modal-height : $menu-height
 			position: absolute
 			right: 10px
 			top: 10px
-			@extend .small
+			@include button-small-basic
 		.bio
 			color: rgba(0, 0, 0, 0.6)
 			font-style: italic
@@ -164,7 +164,7 @@ $header-modal-height : $menu-height
 			position: absolute
 			right: 10px
 			top: 10px
-			@extend .small
+			@include button-small-basic
 		.bio
 			color: rgba(0, 0, 0, 0.6)
 			font-style: italic

sass/style.sass

@@ -443,7 +443,7 @@ textarea.splited-post
 				position: absolute
 				right: 30px
 				top: 10px
-				@extend .small
+				@include button-small-basic
 				display: none
 				padding: .4rem!important
 			&:hover button
@@ -587,7 +587,7 @@ img.twister-user-photo
 				position: absolute
 				right: 30px
 				top: 10px
-				@extend .small
+				@include button-small-basic
 				display: none
 				padding: .4rem!important
 			&:hover button