Change the ‘underline span’ style

The <u> tag is deprecated and WordPress now uses a span with the text-decoration style without class. This is how to target that span and change the style.

span[style*='underline'] {
text-decoration-color: #b22222 !important;
text-decoration-style: dotted !important;
text-decoration-thickness: 2px !important;
}Code language: CSS (css)

Replace the ‘strike though’ style with a background color

span[style*='line-through'] {
text-decoration: unset !important;
background-color: #01f9c6 !important;
}Code language: CSS (css)

Replace the ‘strike though’ style with an offset background color

span[style*='line-through'] {
text-decoration: unset !important;
position: relative;
z-index: 1;
}
span[style*='line-through']::before {
content: '';
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 70%;
background-color: #01f9c6;
z-index: -1;
transform: translate(0.3em, 50%);
}Code language: CSS (css)