Better contrast for input fields (#417)

* Better contrat for input fields

This change set a white background for input field (text, select and textarea)
to have a better contrast with the page background and improve accessibility for
people with vision problem, and just crappy screen.

This change also remove the round corner for the input to have a clear difference
between editing field and buttons.

This max-width of the form element are a bit bigger too.

* Less space between label and input

static/css/main.scss

@@ -4,6 +4,13 @@
 @import url('/static/fonts/Lora/Lora.css');
 @import url('/static/fonts/Playfair_Display/PlayfairDisplay.css');
 
+html {
+  box-sizing: border-box;
+}
+*, *:before, *:after {
+  box-sizing: inherit;
+}
+
 @import 'variables';
 @import 'global';
 @import 'header';