[breaking change] rebuild style struct (#2021)

packages/style/mixins/clearfix.less

@@ -0,0 +1,7 @@
+.clearfix() {
+  &::after {
+    content: '';
+    display: table;
+    clear: both;
+  }
+}

packages/style/mixins/ellipsis.less

@@ -0,0 +1,14 @@
+.multi-ellipsis(@lines) {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  display: -webkit-box;
+  -webkit-line-clamp: @lines;
+  /* autoprefixer: ignore next */
+  -webkit-box-orient: vertical;
+}
+
+.ellipsis() {
+  overflow: hidden;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+}

packages/style/mixins/hairline.less

@@ -0,0 +1,27 @@
+.hairline-common() {
+  content: ' ';
+  position: absolute;
+  pointer-events: none;
+  box-sizing: border-box;
+}
+
+.hairline(@border-color: #eee) {
+  .hairline-common();
+
+  top: -50%;
+  left: -50%;
+  right: -50%;
+  bottom: -50%;
+  transform: scale(0.5);
+  border: 0 solid @border-color;
+}
+
+.hairline-bottom(@border-color: #eee, @left: 0) {
+  .hairline-common();
+
+  left: @left;
+  right: 0;
+  bottom: 0;
+  transform: scaleY(0.5);
+  border-bottom: 1px solid @border-color;
+}