try to fix title (fixed position) inside header

Maths2A/Maths_2A_01_C_Algebre.markdown

@@ -88,7 +88,7 @@ Soit $f \in \mathcal{L}(E)$ un endomorphisme
 
 On considère $(x_1, x_2, ... x_p) = (x_i)_{i\in I}$ une famille de $p$ vecteurs de l'EV $E$
 1. La famille de vecteurs est libre si $\sum\limits_{i=1}^p \lambda_i x_i = 0 \implies \forall i \in I, \lambda_i = 0$ 
-2. La famille de vecteurs est génératrice si $\forall x \in E, \exists (\lambda_i)_{i\in I} / x = \sum\limits_{i=1}^p \lambda_i x_i$
+2. La famille de vecteurs est génératrice si $\forall x \in E, \exists (\lambda_i) i\in I / x = \sum\limits_{i=1}^p \lambda_i x_i$
 3. La famille de vecteurs est une base si elle est libre et génératrice, ou encore si $\forall x \in E, \exists !(\lambda_i), i\in I / x = \sum\limits_{i=1}^p \lambda_i x_i$
 
 **Définitions :**

_includes/header.html

@@ -0,0 +1,31 @@
+<header class="site-header">
+
+    <div class="wrapper">
+      {%- assign default_paths = site.pages | map: "path" -%}
+      {%- assign page_paths = site.header_pages | default: default_paths -%}
+      {%- assign titles_size = site.pages | map: 'title' | join: '' | size -%}
+      <a class="site-title" rel="author" href="{{ "/" | relative_url }}">{{ site.title | escape }}</a>
+  
+      {%- if titles_size > 0 -%}
+        <nav class="site-nav">
+          <input type="checkbox" id="nav-trigger" class="nav-trigger" />
+          <label for="nav-trigger">
+            <span class="menu-icon">
+              <svg viewBox="0 0 18 15" width="18px" height="15px">
+                <path d="M18,1.484c0,0.82-0.665,1.484-1.484,1.484H1.484C0.665,2.969,0,2.304,0,1.484l0,0C0,0.665,0.665,0,1.484,0 h15.032C17.335,0,18,0.665,18,1.484L18,1.484z M18,7.516C18,8.335,17.335,9,16.516,9H1.484C0.665,9,0,8.335,0,7.516l0,0 c0-0.82,0.665-1.484,1.484-1.484h15.032C17.335,6.031,18,6.696,18,7.516L18,7.516z M18,13.516C18,14.335,17.335,15,16.516,15H1.484 C0.665,15,0,14.335,0,13.516l0,0c0-0.82,0.665-1.483,1.484-1.483h15.032C17.335,12.031,18,12.695,18,13.516L18,13.516z"/>
+              </svg>
+            </span>
+          </label>
+  
+          <div class="trigger">
+            {%- for path in page_paths -%}
+              {%- assign my_page = site.pages | where: "path", path | first -%}
+              {%- if my_page.title -%}
+              <a class="page-link" href="{{ my_page.url | relative_url }}">{{ my_page.title | escape }}</a>
+              {%- endif -%}
+            {%- endfor -%}
+          </div>
+        </nav>
+      {%- endif -%}
+    </div>
+  </header>

_layouts/default.html

@@ -173,6 +173,24 @@
 
 {%- include header.html -%}
 
+header {
+  position: fixed;
+  top: 0;
+  width: 100%;
+  z-index: 1000; /* Ensure it stays above other content */
+  background-color: #fff; /* or any background you prefer */
+  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1); /* Optional: adds a shadow to make it stand out */
+}
+
+body {
+  padding-top: 60px; /* Adjust according to your header's height */
+}
+
+body.dark-mode header {
+  background-color: #333;
+  color: white;
+}
+
 <div class="toc">
   <h2 class="no-toc">Sommaire</h2>
   <nav>