diff --git a/src/InputWindowElement.h b/src/InputWindowElement.h
index d35d605..15d5d39 100644
--- a/src/InputWindowElement.h
+++ b/src/InputWindowElement.h
@@ -15,10 +15,12 @@ namespace gj {
 class InputWindowElement : public iElement {
  public:
   struct Param {
+    iAllocator* alloc;
+
     UniqPtr<iInputMatcher>  matcher;
     UniqPtr<iElementDriver> driver;
 
-    Scoreboard* scoreboard = nullptr;
+    Scoreboard* scoreboard;
 
     Period period;
 
@@ -35,13 +37,14 @@ class InputWindowElement : public iElement {
   InputWindowElement(Param&& p) :
       iElement(p.period),
       matcher_(std::move(p.matcher)), drv_(std::move(p.driver)), sb_(p.scoreboard),
-      text_(p.text), expects_(matcher_->expects()) {
+      bg_(CreateEmptySquare_(p.alloc)), text_(p.text), expects_(matcher_->expects()) {
     param_["posX"]  = 0.;
     param_["posY"]  = 0.;
     param_["baseX"] = .5;
   }
 
   void Update(Frame& frame, double t) override {
+    /* consumes all input */
     for (auto c : frame.input) {
       if (matcher_->done()) break;
       if (matcher_->Input(c)) {
@@ -50,18 +53,40 @@ class InputWindowElement : public iElement {
       }
       ++sb_->input;
     }
+
+    /* executes the driver to update parameters and takes them with cast */
     drv_->Update(param_, t);
 
-    const auto posX  = (std::get<double>(param_["posX"])+1)/2;
-    const auto posY  = (std::get<double>(param_["posY"])+1)/2;
+    const auto posX  = std::get<double>(param_["posX"]);
+    const auto posY  = std::get<double>(param_["posY"]);
     const auto baseX = std::get<double>(param_["baseX"]);
 
-    const uint32_t posXi  = static_cast<int32_t>(posX * frame.w);
-    const uint32_t posYi  = static_cast<int32_t>(posY * frame.h);
+    const uint32_t posXi  = static_cast<int32_t>((posX+1)/2 * frame.w);
+    const uint32_t posYi  = static_cast<int32_t>((posY+1)/2 * frame.h);
 
     const uint32_t tbaseXi = static_cast<int32_t>(baseX * text_.width());
     const uint32_t ebaseXi = static_cast<int32_t>(baseX * expects_.width());
 
+    const double w = (4+std::max(text_.width(), expects_.width()))*1. / frame.w;
+    const double h = 4. / frame.h;
+
+    /*  calculates geometry of background rect
+     * and sets alpha to negative to decrease colors of pixels surrounding the text */
+    auto M = mat3{
+      {w, 0, 0},
+      {0, h, 0},
+      {0, 0, 1},
+    };
+    M = ::linalg::mul(mat3{
+      {1, 0, 0},
+      {0, 1, 0},
+      {posX, posY, 1},
+    }, M);
+    bg_.SetMatrix(M);
+    bg_.SetAlpha(-.8f);
+    frame.Add(&bg_);
+
+    /* calculates geometry of foreground text */
     text_.SetPosition(posXi-tbaseXi, posYi);
     expects_.SetPosition(posXi-ebaseXi, posYi+1);
     frame.Add(&text_);
@@ -85,10 +110,17 @@ class InputWindowElement : public iElement {
 
   Scoreboard* sb_;
 
-  Text text_;
-  Text expects_;
+  Texture bg_;
+  Text    text_;
+  Text    expects_;
 
   iElementDriver::Param param_;
+
+  static Colorbuffer CreateEmptySquare_(iAllocator* alloc) {
+    auto buf = Colorbuffer(alloc, 1, 1);
+    buf.ptr()[0] = 1;
+    return std::move(buf);
+  }
 };
 
 
diff --git a/src/InputWindowElementFactory.h b/src/InputWindowElementFactory.h
index d5a58de..9edf95d 100644
--- a/src/InputWindowElementFactory.h
+++ b/src/InputWindowElementFactory.h
@@ -29,6 +29,7 @@ class InputWindowElementFactory : public iElementFactory {
     const std::string kana = std::get<std::string>(param.custom[1]);
 
     InputWindowElement::Param p;
+    p.alloc      = alloc_;
     p.period     = param.period;
     p.scoreboard = sb_;
     p.driver     = std::move(param.driver);