feat(layout): add mix sidebar mode

src/layouts/default/sider/LayoutSider.vue

@@ -128,5 +128,55 @@
   });
 </script>
 <style lang="less">
-  @import './index.less';
+  @import (reference) '../../../design/index.less';
+  @prefix-cls: ~'@{namespace}-layout-sideBar';
+
+  .@{prefix-cls} {
+    z-index: @layout-sider-fixed-z-index;
+
+    &--fixed {
+      position: fixed;
+      top: 0;
+      left: 0;
+      height: 100%;
+    }
+
+    &--mix {
+      top: @header-height;
+      height: calc(100% - @header-height);
+    }
+
+    &.ant-layout-sider-dark {
+      background: @sider-dark-bg-color;
+
+      .ant-layout-sider-trigger {
+        color: darken(@white, 25%);
+        background: @trigger-dark-bg-color;
+
+        &:hover {
+          color: @white;
+          background: @trigger-dark-hover-bg-color;
+        }
+      }
+    }
+
+    &:not(.ant-layout-sider-dark) {
+      // box-shadow: 2px 0 8px 0 rgba(29, 35, 41, 0.05);
+
+      .ant-layout-sider-trigger {
+        color: @text-color-base;
+        border-top: 1px solid @border-color-light;
+      }
+    }
+
+    .ant-layout-sider-zero-width-trigger {
+      top: 40%;
+      z-index: 10;
+    }
+
+    & .ant-layout-sider-trigger {
+      height: 36px;
+      line-height: 36px;
+    }
+  }
 </style>