chore: optimize the code of page width style;

src/layouts/header/AdminHeader.vue

@@ -1,6 +1,6 @@
 <template>
   <a-layout-header :class="[headerTheme, 'admin-header']">
-    <div :class="['admin-header-wide', layout == 'side' ? layout : (pageWidth == 'fixed' ? layout : '')]">
+    <div :class="['admin-header-wide', layout, pageWidth]">
       <router-link v-if="isMobile || layout === 'head'" to="/" :class="['logo', isMobile ? null : 'pc', headerTheme]">
         <img width="32" src="@/assets/img/logo.png" />
         <h1 v-if="!isMobile">{{systemName}}</h1>

src/layouts/header/index.less

@@ -21,7 +21,7 @@
   }
   .admin-header-wide{
     padding-left: 24px;
-    &.head{
+    &.head.fixed{
       max-width: 1400px;
       margin: auto;
       padding-left: 0;