add convertkit signup form

static/style.css

@@ -175,6 +175,43 @@ nav > ul > li > a {
     font-weight: bold;
 }
 
+/* SIGNUP FORM */
+
+.convertkit {
+    margin-top: 3em;
+    padding: 1em;
+    background-color: var(--dim);
+}
+
+.convertkit > p {
+    margin-top: 0;
+}
+
+.convertkit > form {
+    display: flex;
+    margin: 0.5em auto 0 auto;
+    max-width: 30em;
+}
+
+.convertkit > form > input[type=email] {
+    flex-grow: 1;
+    font-size: 1em;
+    padding: 0.5em;
+    margin-right: 0.5em;
+    background: transparent;
+    border: 0;
+    border-bottom: 1px solid var(--deemphasized);
+}
+
+.convertkit > form > button {
+    min-width: 10em;
+    border: 0;
+    border-bottom: 1px solid var(--accent);
+    background: var(--accent);
+    color: var(--text);
+    font-size: 1em;
+}
+
 /* FOOTER */
 
 hr {

templates/convertkit.html

@@ -0,0 +1,11 @@
+<section class="convertkit">
+  <p>
+    Was this helpful?
+    Would you like me to email you things like this a couple times a month?
+    Sign up below and I'll do exactly that!
+  </p>
+  <form action="https://app.convertkit.com/forms/2069198/subscriptions" method="post">
+    <input class="email" name="email_address" aria-label="Email Address" placeholder="Email Address" required="true" type="email" />
+    <button data-element="submit">Subscribe</button>
+  </form>
+</section>

templates/post.html

@@ -22,4 +22,6 @@ <h1>{{ page.title | markdown(inline=true) | safe }}</h1>
 
   {{ page.content | safe }}
 </article>
+
+{% include "convertkit.html" %}
 {% endblock %}