Как сделать овальную форму подписки?

body { 
  background: #ccc; 
} 
 
*{box-sizing: border-box; } 
 
form{ 
  position: relative; 
  max-width: 500px; 
  width: 100%; 
  height: 40px; 
} 
 
input[type="submit"] { 
  background: #fff; 
  border: none; 
  height: 40px; 
  width: 100px; 
  text-align: center; 
  border-radius: 20px; 
  position: absolute; 
  top:0; 
  right: 0; 
  cursor: pointer; 
} 
 
input[type="text"] { 
  height: 40px; 
  width: 100%; 
  border: 1px solid #fff; 
  background: rgba(255,255,255,.25); 
  border-radius: 20px; 
  padding: 10px; 
  padding-right: 100px; 
  outline: none; 
} 
 
/* ---- Placeholder ---- */ 
::-webkit-input-placeholder { 
   color: #000; 
} 
:-moz-placeholder { /* Firefox 18- */ 
   color: #000;   
} 
::-moz-placeholder {  /* Firefox 19+ */ 
   color: #000;   
} 
:-ms-input-placeholder {   
   color: #000;   
} 

<form> 
  <input type="text" placeholder="email adress"> 
  <input type="submit" value="sign up"> 
</form>