[site] Reposition theme changer in site header

Signed-off-by: James Wainwright <james.wainwright@lowrisc.org>

site/landing/assets/scss/_main-header.scss

diff --git a/site/landing/assets/scss/_main-header.scss b/site/landing/assets/scss/_main-header.scss
index 4b7039f..9fa77d1 100644
--- a/site/landing/assets/scss/_main-header.scss
+++ b/site/landing/assets/scss/_main-header.scss
@@ -89,6 +89,13 @@
       padding: 0.25em 0;
       white-space: nowrap;
 
+      svg {
+        vertical-align: bottom;
+        font-size: 1.5em;
+        width: 1em;
+        height: 1em;
+      }
+
       &:after {
         content: "";
         position: absolute;

site/landing/assets/scss/_scheme-toggle.scss

diff --git a/site/landing/assets/scss/_scheme-toggle.scss b/site/landing/assets/scss/_scheme-toggle.scss
index d09edae..fd90609 100644
--- a/site/landing/assets/scss/_scheme-toggle.scss
+++ b/site/landing/assets/scss/_scheme-toggle.scss
@@ -18,8 +18,10 @@
     cursor: pointer;
 
     svg {
-      width: 1.5em;
-      height: 1.5em;
+      vertical-align: bottom;
+      font-size: 1.5em;
+      width: 1em;
+      height: 1em;
       display: block;
       transition: transform 1s cubic-bezier(.18,1.64,.66,.94);
     }