.button-burger -> .nav-button

css/knacss-unminified.css

@@ -2205,8 +2205,8 @@ button:focus {
   -webkit-box-align: stretch;
       -ms-flex-align: stretch;
           align-items: stretch;
-  height: 2.4rem;
-  width: 2.4rem;
+  height: 2.6rem;
+  width: 2.6rem;
   padding: 0;
   background-color: transparent;
   background-image: -webkit-gradient(linear, left top, left bottom, from(#333), to(#333));
@@ -2214,7 +2214,7 @@ button:focus {
   background-position: center;
   background-repeat: no-repeat;
   background-origin: content-box;
-  background-size: 100% calc(2.4rem * (18 / 100));
+  background-size: 100% 5px;
   -webkit-transition: .25s;
   transition: .25s;
   -webkit-transition-property: background, -webkit-transform;
@@ -2226,7 +2226,7 @@ button:focus {
 
 .button-burger > *::before, .button-burger > *::after {
   content: "";
-  height: calc(2.4rem * (18 / 100));
+  height: 5px;
   background: #333;
   -webkit-transition: .25s;
   transition: .25s;