A custom blog theme is an optional customization that can be toggled off or on from your blog settings. When enabled, your theme is how your blog will look at its web address on a regular computer (see ours at staff.tumblr.com). You can choose from tons of themes at www.tumblr.com/themes, and you can always edit your theme from the Customize menu.
If enabled, you can check out a blog’s theme (including your own) by visiting its URL directly (e.g. staff.tumblr.com), or by clicking on that blog in the dashboard, then clicking the URL under the blog's avatar.
To enable or disable custom themes, head to your blog settings on web and switch the “Custom theme” toggle on or off.
Si quieres editar el HTML de tu tema, puedes utilizar el editor, en el apartado de personalización de tu blog. El campo de la descripción también permite incluir HTML, en caso de que necesites añadir pequeños fragmentos de código.
If your theme is mobile responsive you can disable the default theme on mobile browsers in the Customize menu by switching off "Use default mobile theme".
Si quieres consultar qué tipo de código se usa para los temas de Tumblr, echa un vistazo a nuestra guía.