Page to right size (#152)

Reviewed-on: PGL/Clyde#152
Reviewed-by: Maxime <231026@umons.ac.be>
Co-authored-by: Anthony Debucquoy <debucquoy.anthony@gmail.com>
Co-committed-by: Anthony Debucquoy <debucquoy.anthony@gmail.com>

frontend/src/assets/main.css

@@ -1,3 +1,7 @@
+:root {
+	--header-size: 61px;
+}
+
 body {
    background-color: rgb(53, 25, 60);
    margin:0;