Embed an IFrame into Joomla

Inserting iframes is becoming more and more popular. However, for security reasons, some Joomla editors still limit this feature. Unlocking features is also difficult for new users.
The plugin below will help you insert iframes into articles or modules more easily.
Main features of the plugin:
- Works on all versions of Joomla
- Supports inserting Youtube Video, Twitter Feed, Twitter Post.
- Supports embedding of allowed websites
- Only load the embedded page when it's in the user's viewport. Therefore, your web loading speed will not be affected.
- Supports proportional size format. It helps iframes (videos) display better on all devices.
Installing
1. After successfully installing the plugin, go to plugin management > Content - Embed iFrame
2. In here, you set the default size of the iframe. The default size will be used if the system cannot find the iframe's declared size.
There are 2 options to set the size:
- Fixed (Unit: px): Width x Height
- Ratio: Width : Height
For example, you want to display YouTube videos in a 16:9 ratio on all devices. You select "Ratio" and the value is "16:9".

3. Enable plugin to get started.
Using
Go to article management, select the article you want to insert an iframe, add the following short code:
{iframe <URL>|<SIZE:OPTION>}
- <URL>: URL of the website you want to embed. Note that some websites may not be embeddable due to their privacy policies.
- <SIZE>: Optional parameter. If this parameter is not present, the system will use the default size. This parameter has 2 formats:
- [Width]x[Height]: Fixed, Unit px.
- [Width]:[Height]: Dimensions in width/height ratio.
I have been googling how to change the menu colours, as the black text on my purple background is not very readable. However everything I have tried to change the text colour of the Off-Canvas main menu text to white did not work.
Would you know what custom CSS I would need to change all menu items to white text (including submenus).
Probably need background colour to not be white when hovering over submenus
Any help you can provide would be gratefully appreciated (or a pointer to some useful help).
Thank you
see
https://siteupdate.vedicmaths.org/index.php
InPre-Update Check for Joomla 5.4.4
for Off-Canvas it says
Joomla cannot detect the extension's compatibility with the target version of Joomla.
have you implemented the compatibility stuff for Joomla to upgrade extensions correctly ?
Have got two off canvas menus working (1. for tools and 2. for main menu)
However I can only get the Main menu to display the first level of menu items.
Have you any suggestions for getting the sub menu items to display ?
N.B. the menu item with sub menu items does display a down arrow, but trying to click on it only display the item at the main menu level.
see
https://siteupdate.vedicmaths.org/index.php
If you want to see where I have currently got to