styles.css

html {
    margin: 0;
    padding: 0;
    height: 100%;
}

body {
    font-family: 'Arial', sans-serif;
    margin: 0;
    padding: 0;
    background-color: #fdfdfd;
    height: 100%;
}

header {
    background-color: #487591;
    color: #fff;
    text-align: center;
    padding: 1em 0;
}

nav {
    background-color: #365970;
    color: #fff;
    text-align: center;
    padding: 15px 0;
}

nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

nav li {
    display: inline;
    margin-right: 15px;
}

nav a {
    color: #fff;
    text-decoration: none;
    font-weight: bold;
}

nav a:hover {
    border-bottom: 2px solid #fff;
}

.navigation2 nav  {
    background-color: #f5f2f0;
    color: #365970;
    text-align: center;
    padding: 10px 0;
    border-bottom: 1.5px solid #365970;
}

.navigation2 nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.navigation2 nav li {
    display: inline;
    margin-right: 15px;
}

.navigation2 nav a {
    font-size: 14px;
    color: #365970;
    text-decoration: none;
    font-weight: bold;
}

.navigation2 nav a:hover {
    border-bottom: 2px solid #365970;
}


/* Aboutページ */
.intro {
    display: flex;
    align-items: center;
}

.intro-image {
    margin-right: 20px;
}

.intro-image img {
    width: 150px;
    height: 150px;
}


main {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
}

/* Poemsページ */
.poem {
    margin-bottom: 30px;
}

/* Graphicsページ */
.images {
    display: flex;
    flex-direction: row;
    justify-content: center;
    align-items: center;
}

.image {
    margin: 10px;
}

.image img {
    max-width: 100%;
    height: auto; 
}

@media (max-width: 768px) {
    .images {
        flex-direction: column;
    }
    .image {
        max-width: 100%;
    }
}

/* Contactページ */
.form {
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 0;
}

footer {
    background-color: #365970;
    color: #fff;
    text-align: center;
    padding: 1em 0;
}

/* PrismJS 1.29.0
https://prismjs.com/download.html#themes=prism-okaidia&languages=markup+css+clike+javascript+c+python&plugins=line-highlight+remove-initial-line-feed */
/**
 * okaidia theme for JavaScript, CSS and HTML
 * Loosely based on Monokai textmate theme by http://www.monokai.nl/
 * @author ocodia
 */

 code[class*="language-"],
 pre[class*="language-"] {
     color: #f8f8f2;
     background: none;
     text-shadow: 0 1px rgba(0, 0, 0, 0.3);
     font-family: Consolas, Monaco, 'Andale Mono', 'Ubuntu Mono', monospace;
     font-size: 1em;
     text-align: left;
     white-space: pre;
     word-spacing: normal;
     word-break: normal;
     word-wrap: normal;
     line-height: 1.5;
 
     -moz-tab-size: 4;
     -o-tab-size: 4;
     tab-size: 4;
 
     -webkit-hyphens: none;
     -moz-hyphens: none;
     -ms-hyphens: none;
     hyphens: none;
 }
 
 /* Code blocks */
 pre[class*="language-"] {
     padding: 1em;
     margin: .5em 0;
     overflow: auto;
     border-radius: 0.3em;
 }
 
 :not(pre) > code[class*="language-"],
 pre[class*="language-"] {
     background: #272822;
 }
 
 /* Inline code */
 :not(pre) > code[class*="language-"] {
     padding: .1em;
     border-radius: .3em;
     white-space: normal;
 }
 
 .token.comment,
 .token.prolog,
 .token.doctype,
 .token.cdata {
     color: #8292a2;
 }
 
 .token.punctuation {
     color: #f8f8f2;
 }
 
 .token.namespace {
     opacity: .7;
 }
 
 .token.property,
 .token.tag,
 .token.constant,
 .token.symbol,
 .token.deleted {
     color: #f92672;
 }
 
 .token.boolean,
 .token.number {
     color: #ae81ff;
 }
 
 .token.selector,
 .token.attr-name,
 .token.string,
 .token.char,
 .token.builtin,
 .token.inserted {
     color: #a6e22e;
 }
 
 .token.operator,
 .token.entity,
 .token.url,
 .language-css .token.string,
 .style .token.string,
 .token.variable {
     color: #f8f8f2;
 }
 
 .token.atrule,
 .token.attr-value,
 .token.function,
 .token.class-name {
     color: #e6db74;
 }
 
 .token.keyword {
     color: #66d9ef;
 }
 
 .token.regex,
 .token.important {
     color: #fd971f;
 }
 
 .token.important,
 .token.bold {
     font-weight: bold;
 }
 .token.italic {
     font-style: italic;
 }
 
 .token.entity {
     cursor: help;
 }
 
 pre[data-line] {
     position: relative;
     padding: 1em 0 1em 3em;
 }
 
 .line-highlight {
     position: absolute;
     left: 0;
     right: 0;
     padding: inherit 0;
     margin-top: 1em; /* Same as .prism’s padding-top */
 
     background: hsla(24, 20%, 50%,.08);
     background: linear-gradient(to right, hsla(24, 20%, 50%,.1) 70%, hsla(24, 20%, 50%,0));
 
     pointer-events: none;
 
     line-height: inherit;
     white-space: pre;
 }
 
 @media print {
     .line-highlight {
         /*
          * This will prevent browsers from replacing the background color with white.
          * It's necessary because the element is layered on top of the displayed code.
          */
         -webkit-print-color-adjust: exact;
         color-adjust: exact;
     }
 }
 
     .line-highlight:before,
     .line-highlight[data-end]:after {
         content: attr(data-start);
         position: absolute;
         top: .4em;
         left: .6em;
         min-width: 1em;
         padding: 0 .5em;
         background-color: hsla(24, 20%, 50%,.4);
         color: hsl(24, 20%, 95%);
         font: bold 65%/1.5 sans-serif;
         text-align: center;
         vertical-align: .3em;
         border-radius: 999px;
         text-shadow: none;
         box-shadow: 0 1px white;
     }
 
     .line-highlight[data-end]:after {
         content: attr(data-end);
         top: auto;
         bottom: .4em;
     }
 
 .line-numbers .line-highlight:before,
 .line-numbers .line-highlight:after {
     content: none;
 }
 
 pre[id].linkable-line-numbers span.line-numbers-rows {
     pointer-events: all;
 }
 pre[id].linkable-line-numbers span.line-numbers-rows > span:before {
     cursor: pointer;
 }
 pre[id].linkable-line-numbers span.line-numbers-rows > span:hover:before {
     background-color: rgba(128, 128, 128, .2);
 }