引導的大綱按鈕行爲像常規按鈕

我試圖用引導的BTN-大綱初級班做一個好看的按鈕，這樣引導的大綱按鈕行爲像常規按鈕

然而，當我嘗試這樣做，在我HTML代碼

<!DOCTYPE html> 
<html lang="en"> 
    <head> 
     <title></title> 
     <meta charset="utf-8"> 
     <meta name="viewport" content="width=device-width, initial-scale=1"> 
     <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"> 
    </head> 
    <body> 
     <button type="button" class="btn btn-outline-primary">Primary</button> 
     <button type="button" class="btn btn-outline-primary">Primary</button> 
    </body> 
</html>

按鈕出來的固體