const regex = /(>.*?)\QStyle\E([^=][^<]*)/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('(>.*?)\\QStyle\\E([^=][^<]*)', 'gm')
const str = `<div><p style="text-align:left;">Style: <span style="float:right;">Casual</span></p></div><div><p style="text-align:left;">Color: <span style="float:right;">Navy Blue</span></p></div><div><p style="text-align:left;">Pattern Type: <span style="float:right;">Plain</span></p></div><div><p style="text-align:left;">Neckline: <span style="float:right;">Round Neck</span></p></div><div><p style="text-align:left;">Length: <span style="float:right;">Long</span></p></div><div><p style="text-align:left;">Type: <span style="float:right;">A Line</span></p></div><div><p style="text-align:left;">Details: <span style="float:right;">Pearls</span></p></div><div><p style="text-align:left;">Details: <span style="float:right;">Frill</span></p></div><div><p style="text-align:left;">Details: <span style="float:right;">Beaded</span></p></div><div><p style="text-align:left;">Details: <span style="float:right;">Pocket</span></p></div><div><p style="text-align:left;">Sleeve Length: <span style="float:right;">Half Sleeve</span></p></div><div><p style="text-align:left;">Season: <span style="float:right;">Spring/Fall</span></p></div><div><p style="text-align:left;">Composition: <span style="float:right;">75% Cotton</span></p></div><div><p style="text-align:left;">Composition: <span style="float:right;">Denim</span></p></div><div><p style="text-align:left;">Composition: <span style="float:right;">25% Polyester</span></p></div><div><p style="text-align:left;">Fabric: <span style="float:right;">Non-Stretch</span></p></div><div><p style="text-align:left;">Waist Line: <span style="float:right;">Natural</span></p></div><br /><table border="1"><thead><tr><th>size</th><th>Shoulder </th><th>Bust </th><th>Waist Size </th><th>Hip Size </th><th>Sleeve Length </th><th>Length </th><th>Bicep Length </th><th>Cuff </th></tr></thead><tbody><tr><td>XS</td><td> 38 cm</td><td> 91 cm</td><td> 90 cm</td><td> 101 cm</td><td> 39 cm</td><td> 139 cm</td><td> 30 cm</td><td> 25 cm</td></tr><tr><td>S</td><td> 39 cm</td><td> 95 cm</td><td> 94 cm</td><td> 105 cm</td><td> 40 cm</td><td> 140 cm</td><td> 31 cm</td><td> 26 cm</td></tr><tr><td>M</td><td> 40 cm</td><td> 99 cm</td><td> 98 cm</td><td> 109 cm</td><td> 41 cm</td><td> 141 cm</td><td> 32 cm</td><td> 27 cm</td></tr><tr><td>L</td><td> 41 cm</td><td> 103 cm</td><td> 102 cm</td><td> 113 cm</td><td> 42 cm</td><td> 142 cm</td><td> 33 cm</td><td> 28 cm</td></tr></tbody></table>`;
const subst = `$1MODIFIED_COLOR$2`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions