add width trick for mobile background

diff --git a/css/style.css b/css/style.css
index aba0c69..2cca673 100644
--- a/css/style.css
+++ b/css/style.css
@@ -15,6 +15,8 @@
    background-attachment: fixed !important;
    /* background-position: center !important; */
    background-size: cover !important;
+   margin-left: calc(-50vw + 50%);
+   margin-right: calc(-50vw + 50%);
   }
 
 #bg {