Make input file fit in the parent box

issue7734
review49601002

src/sao.less

@@ -125,10 +125,19 @@ input[type='color'] {
 }
 
 .input-file {
-    & input[type='file'] {
+    > input[type='file'] {
         position: absolute;
+        left: 0;
+        top: 0;
+        width: 100%;
+        height: 100%;
         opacity: 0;
         cursor: pointer;
+
+        li& {
+            top: auto;
+            height: auto;
+        }
     }
 }