JSFiddle - React, Tailwind, and code Playground

by AndyE

HTML

<form oninput="valueB.value=+valueA.value+900">
    <input type="number" id="valueA" name="valueA" value="" />
</form>

<form oninput="valueA.value=+valueB.value+300">
    <input type="number" id="valueB" name="valueB" value="" />
</form>

CSS

h1 { 
    position: relative;
    text-align: center;
    color: darkred;
    font-weight: bold;
    background-color: white;
    padding: -50%;
    border-top:1px solid darkred;
}
/*h1:first-line {
}
h1:before {
    position: absolute;
    z-index: -1;
    content: '';
    left: 0px;
    right: 0px;
    height: 1px;
    top: 50%;
    background-color: darkred;    
}
*/