workflow: add stylelint

src/style/index.scss

@@ -26,8 +26,8 @@ label {
 }
 
 *,
-*:before,
-*:after {
+*::before,
+*::after {
   box-sizing: inherit;
 }
 
@@ -55,7 +55,7 @@ ul {
 }
 
 .clearfix {
-  &:after {
+  &::after {
     visibility: hidden;
     display: block;
     font-size: 0;
@@ -97,9 +97,6 @@ ul {
   -moz-filter: grayscale(100%);
   -ms-filter: grayscale(100%);
   -o-filter: grayscale(100%);
-  filter: url("data:image/svg+xml;utf8,#grayscale");
-  filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
-  -webkit-filter: grayscale(1);
 }
 
 // 色弱模式