diff --git a/src/card.ts b/src/card.ts
index ea225cc..bd43f6d 100644
--- a/src/card.ts
+++ b/src/card.ts
@@ -13,7 +13,7 @@ import { EditorView } from '@codemirror/view';
 import { diagnosticsField, setDiagnosticsEffect } from './decoration';
 import type { Diagnostic } from './decoration';
 import { addToDictionary, shouldAddToDict } from './lint';
-import { kindColors, kindColorsDark, fallback, fallbackDark } from './styling';
+import { kindColors, kindColorsDark, fallback, fallbackDark, injectStyleSheet } from './styling';
 
 /** Set `--harper-kind-color` / `--harper-kind-color-dark` CSS custom properties on an element. */
 export function setAccentColor(el: HTMLElement, lintKind: string) {
@@ -188,9 +188,5 @@ export function cardContentCSS(): string {
 
 /** Inject the shared card content CSS once. */
 export function injectCardCSS() {
-  if (document.getElementById('harper-card-base-styles')) return;
-  const style = document.createElement('style');
-  style.id = 'harper-card-base-styles';
-  style.textContent = cardContentCSS();
-  document.head.appendChild(style);
+  injectStyleSheet('harper-card-base-styles', cardContentCSS());
 }
diff --git a/src/extension.ts b/src/extension.ts
index 3166f1c..d6b08e7 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -6,19 +6,14 @@ import { MarkEdit } from 'markedit-api';
 import { diagnosticsField, setDiagnosticsEffect, lintToDiagnostic } from './decoration';
 import { clickTooltipField, tooltipHandlers } from './tooltip';
 import { panelExtension } from './panel';
-import { baseTheme, kindCSS } from './styling';
+import { baseTheme, kindCSS, injectStyleSheet } from './styling';
 import { lint } from './lint';
 import { getProofreadingSettings } from './settings';
 
 const { autoLintDelay } = getProofreadingSettings(MarkEdit.userSettings);
 
 const kindStyleInjector = ViewPlugin.define(() => {
-  if (!document.getElementById('harper-kind-styles')) {
-    const style = document.createElement('style');
-    style.id = 'harper-kind-styles';
-    style.textContent = kindCSS();
-    document.head.appendChild(style);
-  }
+  injectStyleSheet('harper-kind-styles', kindCSS());
   return {};
 });
 
diff --git a/src/menu.ts b/src/menu.ts
index 4f57212..2604fdd 100644
--- a/src/menu.ts
+++ b/src/menu.ts
@@ -26,7 +26,7 @@ export function buildMenuItem(): MenuItem {
       },
       {
         title: 'Reset Dictionary',
-        action: async() => {
+        action: async () => {
           const result = await MarkEdit.showAlert({
             title: 'Are you sure you want to reset the dictionary?',
             message: 'All custom words you have added will be removed. This action cannot be undone.',
@@ -54,8 +54,13 @@ export function buildMenuItem(): MenuItem {
 
 async function proofreadNow() {
   const view = MarkEdit.editorView;
-  const text = view.state.doc.toString();
+  const doc = view.state.doc;
+  const text = doc.toString();
   const lints = await lint(text);
+
+  // Bail out if the document changed during linting
+  if (view.state.doc !== doc) return;
+
   view.dispatch({ effects: setDiagnosticsEffect.of(lints.map(lintToDiagnostic)) });
 }
 
diff --git a/src/panel.ts b/src/panel.ts
index 7bf8151..6d3a403 100644
--- a/src/panel.ts
+++ b/src/panel.ts
@@ -5,6 +5,7 @@ import type { ViewUpdate } from '@codemirror/view';
 import { diagnosticsField, setDiagnosticsEffect } from './decoration';
 import type { Diagnostic } from './decoration';
 import { setAccentColor, findDiagnostic, buildCardContent, injectCardCSS } from './card';
+import { injectStyleSheet } from './styling';
 
 const paneWidth = 290;
 
@@ -562,9 +563,5 @@ export function paneCSS(): string {
 
 function injectPaneCSS() {
   injectCardCSS();
-  if (document.getElementById('harper-pane-styles')) return;
-  const style = document.createElement('style');
-  style.id = 'harper-pane-styles';
-  style.textContent = paneCSS();
-  document.head.appendChild(style);
+  injectStyleSheet('harper-pane-styles', paneCSS());
 }
diff --git a/src/settings.ts b/src/settings.ts
index 5bae35c..ceb2369 100644
--- a/src/settings.ts
+++ b/src/settings.ts
@@ -39,7 +39,7 @@ export function getProofreadingSettings(userSettings: JSONObject | undefined): P
   ) as LintConfig;
 
   const disabledLintKinds = parseStringArray(raw.disabledLintKinds);
-  const addToDict = raw.addToDict === false ? false : true;
+  const addToDict = raw.addToDict !== false;
 
   return { autoLintDelay, lintPreset, lintRuleOverrides, disabledLintKinds, addToDict };
 }
diff --git a/src/styling.ts b/src/styling.ts
index 68c4fc6..133789d 100644
--- a/src/styling.ts
+++ b/src/styling.ts
@@ -92,3 +92,12 @@ export const baseTheme = EditorView.baseTheme({
     transition: 'text-decoration-color 0.15s, background-color 0.15s',
   },
 });
+
+/** Inject a `<style>` element once, keyed by `id`. No-op if already present. */
+export function injectStyleSheet(id: string, css: string): void {
+  if (document.getElementById(id)) return;
+  const style = document.createElement('style');
+  style.id = id;
+  style.textContent = css;
+  document.head.appendChild(style);
+}
diff --git a/src/tooltip.ts b/src/tooltip.ts
index 92cb849..000e134 100644
--- a/src/tooltip.ts
+++ b/src/tooltip.ts
@@ -4,6 +4,7 @@ import type { Tooltip, TooltipView } from '@codemirror/view';
 import { diagnosticsField } from './decoration';
 import type { Diagnostic } from './decoration';
 import { setAccentColor, buildCardContent, ignoreDiagnostic, injectCardCSS } from './card';
+import { injectStyleSheet } from './styling';
 
 export const setClickTooltip = StateEffect.define<Diagnostic | null>();
 
@@ -141,13 +142,7 @@ export const tooltipCSS = `
 
 function createTooltip(view: EditorView, diagnostic: Diagnostic) {
   injectCardCSS();
-
-  if (!document.getElementById('harper-tooltip-styles')) {
-    const style = document.createElement('style');
-    style.id = 'harper-tooltip-styles';
-    style.textContent = tooltipCSS;
-    document.head.appendChild(style);
-  }
+  injectStyleSheet('harper-tooltip-styles', tooltipCSS);
 
   const dom = document.createElement('div');
   dom.className = 'harper-tooltip-wrap';
diff --git a/tests/card.test.ts b/tests/card.test.ts
new file mode 100644
index 0000000..9f92e69
--- /dev/null
+++ b/tests/card.test.ts
@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest';
+import { cardContentCSS } from '../src/card';
+
+describe('cardContentCSS', () => {
+  it('includes message, button, ignore, and actions styles', () => {
+    const css = cardContentCSS();
+    expect(css).toContain('.harper-msg');
+    expect(css).toContain('.harper-btn');
+    expect(css).toContain('.harper-ignore');
+    expect(css).toContain('.harper-actions');
+  });
+
+  it('uses CSS custom properties for accent-colored code', () => {
+    const css = cardContentCSS();
+    expect(css).toMatch(/\.harper-msg\s+code\s*\{[^}]*var\(--harper-kind-color/);
+    expect(css).toMatch(/\.harper-msg\s+code\s*\{[^}]*color-mix/);
+  });
+
+  it('includes hover and active states for buttons', () => {
+    const css = cardContentCSS();
+    expect(css).toContain('.harper-btn:hover');
+    expect(css).toContain('.harper-btn:active');
+    expect(css).toContain('.harper-ignore:hover');
+    expect(css).toContain('.harper-ignore:active');
+  });
+
+  it('includes dark mode overrides', () => {
+    const css = cardContentCSS();
+    expect(css).toContain('@media (prefers-color-scheme: dark)');
+  });
+
+  it('styles ignore button with transparent background and auto margin', () => {
+    const css = cardContentCSS();
+    expect(css).toMatch(/\.harper-ignore\s*\{[^}]*background:\s*transparent/);
+    expect(css).toMatch(/\.harper-ignore\s*\{[^}]*margin-left:\s*auto/);
+  });
+});
diff --git a/tests/kinds.test.ts b/tests/kinds.test.ts
new file mode 100644
index 0000000..669ddec
--- /dev/null
+++ b/tests/kinds.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest';
+import { presetDisabledKinds } from '../src/kinds';
+
+describe('presetDisabledKinds', () => {
+  it('strict disables no kinds', () => {
+    expect(presetDisabledKinds('strict').size).toBe(0);
+  });
+
+  it('standard disables Enhancement, Style, and WordChoice', () => {
+    const kinds = presetDisabledKinds('standard');
+    expect(kinds).toEqual(new Set(['Enhancement', 'Style', 'WordChoice']));
+  });
+
+  it('relaxed includes every standard kind', () => {
+    const standard = presetDisabledKinds('standard');
+    const relaxed = presetDisabledKinds('relaxed');
+
+    for (const kind of standard) {
+      expect(relaxed.has(kind)).toBe(true);
+    }
+  });
+
+  it('relaxed disables more kinds than standard', () => {
+    const standard = presetDisabledKinds('standard');
+    const relaxed = presetDisabledKinds('relaxed');
+    expect(relaxed.size).toBeGreaterThan(standard.size);
+  });
+});
diff --git a/tests/rules.test.ts b/tests/rules.test.ts
new file mode 100644
index 0000000..3cb8efe
--- /dev/null
+++ b/tests/rules.test.ts
@@ -0,0 +1,36 @@
+import { describe, expect, it } from 'vitest';
+import { presetDisabledRules } from '../src/rules';
+
+describe('presetDisabledRules', () => {
+  it('strict disables no rules', () => {
+    expect(presetDisabledRules('strict')).toEqual([]);
+  });
+
+  it('standard disables a non-empty list of rules', () => {
+    const rules = presetDisabledRules('standard');
+    expect(rules.length).toBeGreaterThan(0);
+  });
+
+  it('relaxed includes every standard rule', () => {
+    const standard = presetDisabledRules('standard');
+    const relaxed = presetDisabledRules('relaxed');
+
+    for (const rule of standard) {
+      expect(relaxed).toContain(rule);
+    }
+  });
+
+  it('relaxed disables more rules than standard', () => {
+    const standard = presetDisabledRules('standard');
+    const relaxed = presetDisabledRules('relaxed');
+    expect(relaxed.length).toBeGreaterThan(standard.length);
+  });
+
+  it('contains no duplicate rule names within each preset', () => {
+    for (const preset of ['standard', 'relaxed'] as const) {
+      const rules = presetDisabledRules(preset);
+      const unique = new Set(rules);
+      expect(unique.size).toBe(rules.length);
+    }
+  });
+});
diff --git a/tests/styling.test.ts b/tests/styling.test.ts
index 48c6c01..05dbcee 100644
--- a/tests/styling.test.ts
+++ b/tests/styling.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { kindCSS } from '../src/styling';
+import { kindCSS, kindColors, kindColorsDark } from '../src/styling';
 
 describe('kindCSS', () => {
   it('includes fallback rules and dark mode section', () => {
@@ -14,4 +14,26 @@ describe('kindCSS', () => {
     expect(css).toContain('.cm-harper-lint[data-lint-kind="Style"] { text-decoration: underline solid #C49000aa 2px;');
     expect(css).toContain('.harper-badge[data-kind="Style"] { color: #C49000; background-color: #C4900022; }');
   });
+
+  it('generates rules for every kind in kindColors', () => {
+    const css = kindCSS();
+    for (const kind of Object.keys(kindColors)) {
+      expect(css).toContain(`data-lint-kind="${kind}"`);
+      expect(css).toContain(`data-kind="${kind}"`);
+    }
+  });
+
+  it('includes hover and active states for each kind', () => {
+    const css = kindCSS();
+    for (const kind of Object.keys(kindColors)) {
+      expect(css).toContain(`.cm-harper-lint[data-lint-kind="${kind}"]:hover`);
+      expect(css).toContain(`.cm-harper-lint[data-lint-kind="${kind}"]:active`);
+    }
+  });
+
+  it('every kind in kindColors has a dark variant', () => {
+    for (const kind of Object.keys(kindColors)) {
+      expect(kindColorsDark).toHaveProperty(kind);
+    }
+  });
 });