use b-btn-close in TextCard & fix base height

src/assets/scss/main.scss

@@ -7,8 +7,13 @@ html, body, #app {
   height: 100%;
 }
 
+#app {
+  display: flex;
+  flex-direction: column;
+}
+
 main {
-  height: calc(100vh - 56px);
+  height: 100%;
 }
 
 // Layouts

src/components/text/TextCard.vue

@@ -23,9 +23,7 @@
               {{ child.id }}
             </b-nav-item>
 
-            <b-nav-item @click="$emit('close', id)">
-              x
-            </b-nav-item>
+            <b-button-close @click="$emit('close', id)" />
           </b-nav>
         </b-card-header>