Add link underline styles for accessibility

Fixes #106
Fixes #44

Author: sindresorhus

constants.js

@@ -96,6 +96,11 @@ export const ALLOW_CLASS = new Set([
 const octicon = String.raw`<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' version='1.1' aria-hidden='true'><path fill-rule='evenodd' d='M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z'></path></svg>`;
 
 export const manuallyAddedStyle = `
+.markdown-body a {
+  text-decoration: underline;
+  text-underline-offset: .2rem;
+}
+
 .markdown-body .octicon {
   display: inline-block;
   fill: currentColor;

test.js

@@ -110,6 +110,22 @@ test('transparentBackground - onlyVariables', async () => {
 	assert.ok(css.includes('--bgColor-default: transparent'), 'should set --bgColor-default to transparent');
 });
 
+test('link underline styles are included', async () => {
+	const css = await githubMarkdownCss();
+	assert.ok(css.includes('.markdown-body a {\n  text-decoration: underline;'), 'should include link underline styles');
+	assert.ok(css.includes('text-underline-offset'), 'should include underline offset');
+});
+
+test('link underline styles in onlyStyles mode', async () => {
+	const css = await githubMarkdownCss({onlyStyles: true});
+	assert.ok(css.includes('.markdown-body a {\n  text-decoration: underline;'), 'should include link underline styles in onlyStyles mode');
+});
+
+test('no link underline styles in onlyVariables mode', async () => {
+	const css = await githubMarkdownCss({onlyVariables: true});
+	assert.ok(!css.includes('text-underline-offset'), 'should not include link styles in onlyVariables mode');
+});
+
 test('no transparentBackground by default', async () => {
 	const css = await githubMarkdownCss();
 	assert.ok(!css.includes('--bgColor-default: transparent'), 'should not have transparent background by default');