<!DOCTYPE html>

<html>
  <head>
    <meta charset="UTF-8" />
    <meta name="description" content="A free offline anime watching website"/>
    <meta name="keywords" content="anime, plus, anime+"/>
    <meta name="author" content="Gavin Horrocks"/>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  
    <link rel="stylesheet" href="style.css">
    <link rel="script" href="script.js">
  </head>

  <body>
    <h1>
      <center>Anime+</center>
    </h1>
    
    <h2>
      <center>this is a offline app to watch anime on.</center>
    </h2>

    <p style="font-size: 20px; color:#1F9AFE;">
    <a href="subpages/attack-on-titan/attack-on-titan-ep1.html">Episode 1</a>
    </p>

    <button onclick="episode1" class="button button1">Episode 1</button>
  </body>
</html>
html {
    min-height: 100%;
    background: grey;
}

h1 {
    color: white;
}

h2 {
    color: white;
}

h3 {
    color: white;
}

h4 {
    color: white;
}

h5 {
    color: white;
}

h6 {
    color: white;
}

.button {
    border: black;
    color: white;
    padding: 15px 32px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 16px;
    margin: 4px 2px;
    cursor: pointer;
}

.button1 {
    background-color: white;
    color: black;
    border: 2px black;
}

.button1:hover {
    background-color: gray;
}
<html>
  <head>
    <meta charset="UTF-8" />
    <meta name="description" content="A free offline anime watching website"/>
    <meta name="keywords" content="anime, plus, anime+"/>
    <meta name="author" content="Gavin Horrocks"/>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  
    <link rel="stylesheet" href="style.css">
    <link rel="script" href="script.js">
  </head>
  <body>
    <iframe width="420" height="315"
      src="https://invidious.fdn.fr/embedded/watch?v=tQw3oYUTejs">
    </iframe>
  </body>
<html>