diff --git a/.gitrev b/.gitrev
index acb63d8..ddb6882 100644
--- a/.gitrev
+++ b/.gitrev
@@ -1 +1 @@
-18e927e
+e57c18a
diff --git a/poisson/index.html b/poisson/index.html
index 89d4da2..63f0c38 100644
--- a/poisson/index.html
+++ b/poisson/index.html
@@ -28,8 +28,8 @@
         <input type="button" title='r' class="button" id="button_restart" value="restart" onclick="pressButton('r')">
       </div>
       <div class="row">
-        <span class="kbdspan"><kbd>click</kbd> draw mask</span>,
-        <span class="kbdspan"><kbd>space</kbd> toggle pause</span>,
+        <span class="kbdspan"><kbd>click</kbd> draw mask (imposes zero solution),</span>
+        <span class="kbdspan"><kbd>space</kbd> toggle pause,</span>
         <span class="kbdspan"><kbd>r</kbd> restart</span>
       </div>
       <div class="row" id="text_status"></div>
diff --git a/poisson/poisson.css b/poisson/poisson.css
index f414ec7..34102ea 100644
--- a/poisson/poisson.css
+++ b/poisson/poisson.css
@@ -15,6 +15,7 @@ html, body {
   margin-top: 0;
   padding: 0.5em;
   text-align: center;
+  max-width: 500px;
 }
 .row {
   margin: 0.5em 0 0.5em 0;