Supersize: Fix broken unit select styling.

Fix suggested by Tiger in crrev.com/c/1240503.

Change-Id: Id7881a60bcc62bf0526c82e80b469db03e350044
Reviewed-on: https://chromium-review.googlesource.com/c/1286929Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600456}

tools/binary_size/libsupersize/static/viewer.html

@@ -95,7 +95,7 @@ if ('serviceWorker' in navigator) {
         <label class="checkbox-label" for="methodcount">Method Count Mode</label>
       </div>
       <p class="select-wrapper">
-        <select id="byteunit" name="byteunit" data-dynamic>
+        <select id="byteunit" class="sel-big" name="byteunit" data-dynamic>
           <option value="B">B - bytes</option>
           <option value="KiB" selected>KiB - kibibytes</option>
           <option value="MiB">MiB - mebibytes</option>