added file to overwrite the style settings in main theme css

src/Presentation/Nop.Web/Nop.Web.csproj

@@ -44,6 +44,8 @@
 
     <!-- We copy the \Logs directory -->
     <Content Include="Logs\**" CopyToPublishDirectory="PreserveNewest" />
+    <Content Remove="Themes\DefaultClean\Content\css\custom.css" />
+    <Content Remove="Themes\DefaultClean\Content\css\styles.css" />
     <Content Remove="Themes\DefaultClean\Content\images\logo.png" />
     <Content Remove="Themes\DefaultClean\Content\images\TheGoodwoodFlooringCompany_Logo 2021_RGB.png" />
     <Content Remove="wwwroot\css\admin\images\logo.png" />

src/Presentation/Nop.Web/Themes/DefaultClean/Content/css/custom.css

@@ -0,0 +1,20 @@
+body {
+}
+
+/*customisations*/ 
+
+.header {
+  position: relative;
+  z-index: 10;
+  width: 100%;
+  margin: 0;
+  text-align: center;
+}
+
+.header-upper {
+  position: sticky !important;
+  z-index: 1;
+  border-bottom: 1px solid #ddd;
+  background-color: #0d4828;
+  color: wheat;
+}