update

src/Presentation/Nop.Web/Themes/test theme/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: fixed;
+  z-index: 1;
+  border-bottom: 1px solid #ddd;
+  background-color: #0d4828;
+  color: wheat;
+}

src/Presentation/Nop.Web/Themes/test theme/Content/css/print.css

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+
+body {
+	font: normal 9pt Arial, Helvetica, sans-serif;
+	color: #000;
+}
+table {
+	width: 100%;
+	border: 0;
+	border-collapse: collapse;
+	border-spacing: 0;
+}
+li {
+	list-style: none;
+}
+a {
+	color: inherit;
+}
+
+.order-details-page .order-overview {
+	margin: 0 0 25px;
+}
+.order-details-page .order-overview .order-number {
+	font-size: 11pt;
+	text-transform: uppercase;
+    padding: 10px 40px;
+}
+.order-details-page .order-overview .order-total {
+	margin: 10px 0 0;
+}
+.order-details-page .order-overview .order-total strong {
+	font-size: 10pt;
+}
+
+.order-details-page .order-details-area {
+	margin: 0 0 25px;
+	overflow: hidden;
+}
+.order-details-page .order-details-area ul {
+    padding-left: 0px;
+}
+.order-details-page .order-details-area > div {
+	float: left;
+	width: 48%;
+	margin: 0 1% 40px;
+}
+.order-details-page .order-details-area li.title {
+	margin: 10px 0 5px;
+	font-weight: bold;
+}
+.order-details-page .order-details-area li:first-child {
+	margin-top: 0;
+}
+
+.order-details-page .data-table {
+	border: 1px solid;
+}
+.order-details-page .data-table th {
+	border-right: 1px solid;
+	border-bottom: 1px solid;
+	padding: 5px 10px;
+	font-weight: bold;
+	white-space: nowrap;
+}
+.order-details-page .data-table td {
+	border-right: 1px solid;
+	border-bottom: 1px solid;
+	padding: 5px 10px;
+}
+.order-details-page .data-table .sku,
+.order-details-page .data-table .unit-price,
+.order-details-page .data-table .quantity,
+.order-details-page .data-table .total {
+    white-space: nowrap;
+    text-align: center;
+}
+.order-details-page .data-table .unit-price,
+.order-details-page .data-table .quantity,
+.order-details-page .data-table .total {
+	width: 15%;
+}
+.order-details-page .data-table label {
+	display: none;
+}
+
+.order-details-page .section {
+	margin: 30px 0;
+}
+.order-details-page .section .title {
+	margin: 0 0 10px;
+}
+.order-details-page .tax-shipping-info,
+.order-details-page .selected-checkout-attributes {
+	margin: 20px 0;
+	text-align:right;
+}
+
+.order-details-page .cart-total-right {
+    white-space: nowrap;
+}
+.order-details-page .cart-total td {
+	padding: 5px 10px;
+	text-align: right;
+}
+.order-details-page td.cart-total-left {
+	width: 100%;
+	font-weight: bold;
+}

src/Presentation/Nop.Web/Themes/test theme/Content/css/styles.css

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+@import url("standard.css");
+@import url("custom.css");

src/Presentation/Nop.Web/Themes/test theme/Views/Shared/Head.cshtml

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+@inject IThemeContext themeContext
+
+@{
+    var themeName = await themeContext.GetWorkingThemeNameAsync();
+
+    //add main CSS file
+    if (await Html.ShouldUseRtlThemeAsync(themeName))
+    {
+        Html.AppendCssFileParts($"~/Themes/{themeName}/Content/css/styles.rtl.css");
+    }
+    else
+    {
+        Html.AppendCssFileParts($"~/Themes/{themeName}/Content/css/styles.css");
+    }
+
+    //add jQuery UI css file
+    Html.AppendCssFileParts("~/lib_npm/jquery-ui-dist/jquery-ui.min.css");
+}

src/Presentation/Nop.Web/Themes/test theme/Views/_ViewImports.cshtml

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+@inherits Nop.Web.Framework.Mvc.Razor.NopRazorPage<TModel>
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+@*we remove the default InputTagHelper to prevent the checkbox duplicating: https://stackoverflow.com/questions/42544961/asp-net-core-custom-input-tag-helper-rendering-duplicate-checkboxes*@
+@removeTagHelper Microsoft.AspNetCore.Mvc.TagHelpers.InputTagHelper, Microsoft.AspNetCore.Mvc.TagHelpers
+@addTagHelper *, Nop.Web.Framework
+@addTagHelper *, MiniProfiler.AspNetCore.Mvc
+
+@using System.Globalization;
+@using Microsoft.AspNetCore.Mvc.ViewFeatures
+@using Microsoft.Extensions.Primitives
+@using Nop.Web.Extensions
+@using Nop.Web.Framework
+@using Nop.Web.Framework.Extensions
+@using Nop.Web.Framework.Infrastructure
+@using Nop.Web.Framework.Models
+@using Nop.Web.Framework.Security.Captcha
+@using Nop.Web.Framework.Security.Honeypot
+@using Nop.Web.Framework.Themes
+@using Nop.Web.Framework.UI
+@using Nop.Web.Models.Blogs
+@using Nop.Web.Models.Boards
+@using Nop.Web.Models.Catalog
+@using Nop.Web.Models.Checkout
+@using Nop.Web.Models.Cms
+@using Nop.Web.Models.Common
+@using Nop.Web.Models.Customer
+@using Nop.Web.Models.Media
+@using Nop.Web.Models.News
+@using Nop.Web.Models.Newsletter
+@using Nop.Web.Models.Order
+@using Nop.Web.Models.Polls
+@using Nop.Web.Models.PrivateMessages
+@using Nop.Web.Models.Profile
+@using Nop.Web.Models.ShoppingCart
+@using Nop.Web.Models.Topics
+@using Nop.Web.Models.Vendors

src/Presentation/Nop.Web/Themes/test theme/theme.json

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+{
+  "SystemName": "test theme",
+  "FriendlyName": "Test Theme",
+  "SupportRTL": true,
+  "PreviewImageUrl": "~/Themes/DefaultClean/preview.jpg",
+  "PreviewText": "my test theme"
+}