improve preview styles

web/app/components/input/__preview-wrapper/input__preview-wrapper.scss

@@ -0,0 +1,4 @@
+.input__preview-wrapper {
+  overflow: hidden;
+  background: #eee;
+}

web/app/components/input/__preview/input__preview.scss

@@ -1,6 +1,7 @@
 .input__preview {
   margin-top: 8px;
   padding: 7px 11px;
+  overflow: hidden;
   font-size: 16px;
   line-height: 1.2;
   border: 1px dashed #eee;

web/app/components/input/index.js

@@ -14,3 +14,4 @@ require('./__error/input__error.scss');
 require('./__field/input__field.scss');
 require('./__field-wrapper/input__field-wrapper.scss');
 require('./__preview/input__preview.scss');
+require('./__preview-wrapper/input__preview-wrapper.scss');

web/app/components/input/input.jsx

@@ -149,10 +149,12 @@ export default class Input extends Component {
           // TODO: it can be more elegant;
           // for example it can render full comment component here (or above textarea on mobile)
           !!preview && (
-            <div
-              className={b('input__preview', { mix: 'raw-content' })}
-              dangerouslySetInnerHTML={{ __html: preview }}
-            />
+            <div className="input__preview-wrapper">
+              <div
+                className={b('input__preview', { mix: 'raw-content' })}
+                dangerouslySetInnerHTML={{ __html: preview }}
+              />
+            </div>
           )
         }
       </form>