C41: fix change of contrast ratio in Procedure

[momdo]

https://www.w3.org/WAI/WCAG22/Techniques/css/C41#tests

The required change of contrast for Focus Appearance (Minimum) is 3:1, this technique goes slightly beyond the minumum requirement.

The success criterion "Focus Appearance (Minimum)" was renamed "Focus Appearance," and "Focus Appearance (Enhanced)" was deleted.
Therefore, the change of contrast ratio shown in the procedure should be 3:1 instead of 4.5:1.

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[patrickhlauke]

while we're here ... the hex values in the code sample don't match the image that's then shown in the example.

The code sample uses

background-color: #236AB8; /* medium-dark blue */

outline: 3px #fff5be solid; /* light yellow */

but the example in the image actually uses

background-color: #003366; /* dark blue */

outline: 3px #ffff00 solid; /*yellow */

Suggest changing the example code as well (yes, the example then has a contrast ratio of 11.7:1 ... but this still gives a good example of a strong focus indicator)