Started styling the app and have got editing posts working.

assets/css/main.css

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+html {
+    font-family: -apple-system, BlinkMacSystemFont, "Avenir Next", Avenir,
+        "Nimbus Sans L", Roboto, "Noto Sans", "Segoe UI", Arial, Helvetica,
+        "Helvetica Neue", sans-serif;
+}
+
+body.role-site {
+    display: flex;
+    flex-direction: column;
+}
+
+body.role-site header {
+    display: flex;
+    flex-direction: row;
+    justify-content: space-between;
+    align-items: center;
+
+    padding-block: 1rem;
+}
+
+body.role-site header h1 {
+    margin-block: 0;
+}
+
+body.role-site .client-area {
+    flex-grow: 1;
+    flex-shrink: 1;
+
+    display: flex;
+    flex-direction: row;
+}
+
+body.role-site nav.vert {
+    width: 150px;
+}
+
+body.role-site main {
+    flex-grow: 1;
+    flex-shrink: 1;
+}
+
+
+
+form.post-form {
+    display: flex;
+    flex-direction: column;
+    height: 100%;
+}
+
+form.post-form textarea {
+    flex-grow: 1;
+    flex-shrink: 1;
+}

assets/css/reset.css

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+
+/* Box sizing rules */
+*,
+*::before,
+*::after {
+    box-sizing: border-box;
+}
+
+/* Prevent font size inflation */
+html {
+    -moz-text-size-adjust: none;
+    -webkit-text-size-adjust: none;
+    text-size-adjust: none;
+}
+
+/* Remove default margin in favour of better control in authored CSS */
+body, h1, h2, h3, h4, p,
+figure, blockquote, dl, dd {
+    margin-block-end: 0;
+}
+
+/* Remove list styles on ul, ol elements with a list role, which suggests default styling will be removed */
+ul[role='list'],
+ol[role='list'] {
+    list-style: none;
+}
+
+/* Set core body defaults */
+body {
+    min-height: 100vh;
+    margin-block: 0;
+    line-height: 1.5;
+}
+
+/* Set shorter line heights on headings and interactive elements */
+h1, h2, h3, h4,
+button, input, label {
+    line-height: 1.1;
+}
+
+/* Balance text wrapping on headings */
+h1, h2,
+h3, h4 {
+    text-wrap: balance;
+}
+
+/* A elements that don't have a class get default styles */
+a:not([class]) {
+    text-decoration-skip-ink: auto;
+    color: currentColor;
+}
+
+/* Make images easier to work with */
+img,
+picture {
+    max-width: 100%;
+    display: block;
+}
+
+/* Inherit fonts for inputs and buttons */
+input, button,
+textarea, select {
+    font-family: inherit;
+    font-size: inherit;
+}
+
+/* Make sure textareas without a rows attribute are not tiny */
+textarea:not([rows]) {
+    min-height: 10em;
+}
+
+/* Anything that has been anchored to should have extra scroll margin */
+:target {
+    scroll-margin-block: 5ex;
+}
+