Use proper button groups

Improve styling of button groups, so they're more intuitive. Remove
button-group containers for single buttons.

app/components/file-preview/component.js

@@ -123,7 +123,7 @@ export default Component.extend({
                 showEditor: false
               });
             }).catch(err => {
-              alert('Failed to update the file. Check the console for more info');
+              alert('Failed to update the file. Check the console for more info.');
               console.error(err);
             });
       } else {

app/styles/_buttons.scss

@@ -1,24 +1,16 @@
-div.button-group {
-  display: inline-block;
-}
-
-div.button-group + button,
-div.button-group + div.button-group {
-  margin-left: 1rem;
-}
-
 header {
+
   button, a.button {
     display: inline-block;
     padding: 0.4rem 0 0.3rem;
-    text-align: center;
+    width: 3rem;
     border: 1px solid $dark-grey-2;
     border-radius: 0.2em;
     background-color: #fff;
     color: $dark-grey-2;
+    text-align: center;
     font-size: 0.8rem;
     text-transform: uppercase;
-    width: 3rem;
 
     svg {
       height: 1rem;
@@ -38,8 +30,8 @@ header {
       }
     }
 
-    &:disabled,
+    &:disabled:not(.active),
-    &:disabled:hover {
+    &:disabled:not(.active):hover {
       border-color: $dark-grey-3;
       background-color: #fff;
       color: $dark-grey-3;
@@ -50,5 +42,47 @@ header {
         }
       }
     }
+
+    &.active {
+      border-color: lighten($dark-grey-2, 10%);
+      background-color: lighten($dark-grey-2, 10%);
+      color: lighten($dark-grey-2, 10%);
+
+      svg {
+        path {
+          fill: #fff;
         }
+      }
+    }
+  }
+
+  button + .button-group,
+  .button-group + button,
+  .button-group + .button-group {
+    margin-left: 1rem;
+  }
+
+  .button-group {
+    position: relative;
+    display: inline-flex;
+    flex-direction: row;
+
+    button {
+      position: relative;
+      margin-right: 0;
+      flex: 0 1 auto;
+
+      &:not(:last-child) {
+        border-top-right-radius: 0;
+        border-bottom-right-radius: 0;
+      }
+    }
+
+    button + button {
+      margin-left: -1px;
+      border-top-left-radius: 0;
+      border-bottom-left-radius: 0;
+    }
+  }
+
 }

app/templates/inspect.hbs

@@ -1,7 +1,6 @@
 <header>
   {{breadcrumb-nav currentDirPath=currentDirPath}}
   <nav class="actions">
-    <div class="button-group">
     {{#if metadataHidden}}
       <button {{action "toggleMetadata"}}
               title="Show metadata">
@@ -13,14 +12,11 @@
         {{partial "icons/arrow-to-right"}}
       </button>
     {{/if}}
-    </div>
     {{#if publicItemURL}}
-      <div class="button-group">
       <a class="button" href={{publicItemURL}} target="_blank"
          title="Open document in new tab">
           {{partial "icons/share"}}
       </a>
-      </div>
     {{/if}}
     {{#if documentIsJSON}}
       <div class="button-group json-view">