private void numNumOfStroke_Enter(object sender, EventArgs e)
{
txtKana.Text = "";
Placeholder.leave_event_placeholder(txtKana, "Hiragana/Katakana");
txtMeaning.Text = "";
}
private void txtKana_Leave(object sender, EventArgs e)
{
Placeholder.leave_event_placeholder(txtKana, "Hiragana/Katakana");
}