Increase size of Simple List Title

You can use this CSS code.

#1. All Simple Lists

h2.list-item-content__title {
font-size: 30px !important;
}

#2. Simple Lists on One Page

First, you need to find the Page ID. Use below tool.

In my example, we will have:

Next, use CSS code:

#collection-66aef2caff007776a825a948 h2.list-item-content__title {
font-size: 30px !important;
}

#3. Specific Simple List

First, you need to find the Simple List ID. Use #2 tool. In my example, we will have:

Next, use this CSS code

section[data-section-id="66b15cf3636b196012828b12"] h2.list-item-content__title {
font-size: 30px !important;
}

#4. Mobile only

@media screen and (max-width:767px) {
h2.list-item-content__title {
font-size: 30px !important;
}}

#5. Desktop Only

@media screen and (min-width:768px) {
h2.list-item-content__title {
font-size: 30px !important;
}}