A few modification

main.css

@@ -18,17 +18,32 @@ html, body{
 #header {
     display: flex;
     flex-direction: row;
-    padding: 30px;
+    padding: 3px;
     background-color: blanchedalmond;
 }
 
 #logo {
+    flex:1;
+    background-color: aqua;
     background-image: url("Logo.jpg");
-    background:no-repeat;
+    /*background:no-repeat;*/
+}
+
+.logo{
+    height: 100%;
+    width: 100%;
 }
 
 #nav {
     background-color: yellow;
+    flex: 9;
+    text-align: initial;
+    letter-spacing: 2px;
+    padding: 10px;
+}
+
+.nav-element {
+    padding: 10px;
 }
 
 /*Body et son contenu */
@@ -63,6 +78,7 @@ body {
     height: 100%;
     border: 1px solid rgba(0,0,0,.125);
     border-radius: .25rem;
+    overflow: scroll;
 }
 
 /*Footer et son contenue*/