Kiln, A letter from the studio

What the HTML does

• Table layout with ghost tables for Outlook. Columns are tables inside Outlook-only conditional comments, so Word's engine gets the widths it needs and everyone else gets the responsive version.
• VML buttons. Each button is a VML shape for Outlook and a padded link everywhere else, so the whole button is clickable in both.
• Dark-mode meta. color-scheme and supported-color-schemes tell Apple Mail and Outlook how the email expects to be treated in dark mode.
• Preheader. The preview text is in the HTML, hidden from the body, so the inbox shows what you wrote instead of the first line of the footer.
• Mobile stacking. Columns stack under 600px with a media query, and stay side by side where media queries are ignored.
• Inline styles. Every style that matters is on the element, because Gmail strips most of the head and some clients drop it entirely.
• Exact line heights in Outlook. mso-line-height-rule: exactly keeps spacers and text from drifting in Outlook for Windows.
• Outlook DPI fix. The OfficeDocumentSettings block stops Outlook from scaling images on high-DPI Windows displays.
• Presentation tables. Layout tables carry role="presentation" so screen readers read the content, not the grid.