The Simple Custom Content Adder (SCCA) does exactly what it says on the tin – adds some custom content to all of your posts and pages, simply.

Write it once and it appears everywhere you asked for it. Change it once and every post and page changes with it. That is the whole idea: a disclaimer at the foot of every post, a promotion above every page, a sign-up prompt under every article – without touching your theme or editing a single post.

Write it in the editor you already know

Your content is written in the full WordPress editor, so you get bold and italics, links, lists, headings and the Add Media button. Paste in HTML if you prefer, and shortcodes from your other plugins work inside the box too.

Put it where you want it

Automatically – tick Posts and/or Pages, then choose whether the box sits before your content, after it, or both.
The Custom Content block – drop it exactly where you want it in the block editor, mid-article if you like. It supports wide and full alignment and the block editor’s own margin controls.
[scca] – the same box as a shortcode, for the classic editor, widgets, templates and page builders.
[scca_hide] – leave the box off one particular post or page.

Where a post uses the block or either shortcode, the automatic copy is left off, so your content never turns up twice on the same page.

Style it without writing CSS

Background colour, text colour, border colour and width, padding, font size, rounded corners and their radius, maximum width and alignment are all set with pickers and fields on the settings screen. A live preview sits at the top of the styling panel and updates as you change each value, so you can see the finished box before you save it.

Or write the CSS yourself

Two escape hatches for anyone who would rather be precise:

Additional CSS is appended to the styles the plugin generates, so you can adjust one detail without rebuilding the rest.
Custom CSS replaces the generated styles entirely, and the styling options step aside.

Built to stay out of the way

Settings are stored in a single record, sanitised on save and escaped on output.
The admin styles and scripts load only on the plugin’s own settings screen, and nothing is fetched from a third-party CDN.
The box is plain HTML with no per-visitor content, so it caches safely.
The content filter priority can be raised or lowered when another plugin insists on inserting its own content in the wrong place.
Every string is translatable.