Update SCSS to module system (fixes #266)

Change-Id: I2387ef49dadaeac0f62620e0c803df12dad42cf8
diff --git a/dev/scss/main/panel.scss b/dev/scss/main/panel.scss
index 568ba5b..94893b9 100644
--- a/dev/scss/main/panel.scss
+++ b/dev/scss/main/panel.scss
@@ -1,4 +1,5 @@
-@import "../util";
+@use "../util";
+@use "../base/lengths";
 
 /**
  * Base styles for all panels and views,
@@ -13,7 +14,7 @@
 
 div.view {
   position:    relative;
-  padding-top: $border-size;
+  padding-top: lengths.$border-size;
   display:     block;
   width:       100%;
 }